In January I compiled a list of education related Google+ communities in this Google document. I then added another 30 communities in May, bringing the list to over 80 Google+ communities now, which is copied below and ordered by their number of members.
UPDATE May 2015: There are now over 1.4 Million members in over 200 educational Google+ communities listed in the spreadsheet.
UPDATE November 2014: I now have the list of education related Google+ communities in a spreadsheet, with up to date membership numbers. There are now over 190 communities listed with over 350,000 members.
The new spreadsheet is at: http://bit.ly/edugoogleplus
If you know of other educational Google+ communities, please fill out this form: http://bit.ly/edugoogleplusform
My Own Google+ Communities
Here are some I started – anyone’s welcome to contribute:
Physics Education (1616 members)
https://plus.google.com/communities/104420542322354041818
Open Source in Education (575 members)
https://plus.google.com/communities/106481215923304023917
Educational Psychology & the Learning Sciences (442 members)
https://plus.google.com/communities/110344341552679196162
Embodied Cognition (71 members) [not specifically about education, but I post a lot of articles related to education there]
https://plus.google.com/communities/101567568840976715864
New Educational Google+ Communities Added in November, 2013
Google Apps in Education [missed this one earlier] (22,020 members)
https://plus.google.com/communities/111138038754004333717
The Center [for faculty & staff at CA community colleges] (109 members)
https://plus.google.com/communities/100765743403325466833
STEM Education Research (95 members)
https://plus.google.com/communities/117133642954138057221
Blockly users (68 members)
https://plus.google.com/communities/118053978752868034148
OER University (30 members)
https://plus.google.com/communities/111229013331366017087
(and there are several other new educational Google+ communities – I just haven’t been actively searching for them – feel free to comment if you know of more)
New Educational Google+ Communities Added in May, 2013
[The number of members is from May]
Learning Creative Learning (10704 members)
https://plus.google.com/u/0/communities/106132864609383396284
Chromebook EDU (2494 members)
https://plus.google.com/u/0/communities/111885171520981887334
Mozilla Webmakers (1500 members)
https://plus.google.com/u/0/communities/106022863174952221205
Gamification in Education (853 members)
https://plus.google.com/u/0/communities/114370132276739546873
STEM Educators (835 members)
https://plus.google.com/u/0/communities/112904336188381403474
Using Google Apps as a Free LMS (707 members)
https://plus.google.com/u/0/communities/110147344160609001644
Apps Scripts for Education – Builders and Users (491 members)
https://plus.google.com/u/0/communities/112780694700423616523
Minecraft in Education (370 members)
https://plus.google.com/u/0/communities/113884091278414495934
Peeragogy in Action (368 members)
https://plus.google.com/u/0/communities/107386162349686249470
Instructional Technology Integrators & Coaches (293 members)
https://plus.google.com/u/0/communities/118257375639026937151
Cognitive Science and Writing (235 members)
https://plus.google.com/u/0/communities/100746062204320903342
Open Education (206 members)
https://plus.google.com/u/0/communities/102204610906149781269
Instruction Librarians (180 members)
https://plus.google.com/u/0/communities/105701165713397630072
EdTech and Professional Development (153 members)
https://plus.google.com/communities/108369417825821080542
Learning Design and Technology – Open Mic (151 members)
https://plus.google.com/u/0/communities/108092082832559743776
Web Accessibility (140 members)
https://plus.google.com/u/0/communities/107472407495224690148
Mathematics Education Research (121 members)
https://plus.google.com/u/0/communities/104846032595782747037
EdTechTalk (100 members)
https://plus.google.com/u/0/communities/102307879401185751970
Educational technology research (96 members)
https://plus.google.com/u/0/communities/116645258659907675031
STEM Education Research (95 members)
https://plus.google.com/communities/117133642954138057221
Online Course Design and Instruction (69 members)
https://plus.google.com/u/0/communities/102383725482697646879
Math Principles in Everyday Life (66 members)
https://plus.google.com/u/0/communities/102010799601556689266
Drupal in Education (64 members)
https://plus.google.com/u/0/communities/102902903124131117699
OCTEL Open Course in Technology Enhanced Learning (58 members)
https://plus.google.com/u/0/communities/101382199434711534938
Google+ for Higher Education (53 members)
https://plus.google.com/u/0/communities/109765983572507353761
SMEDU Social Media in Education (47 members)
https://plus.google.com/u/0/communities/108334907562991099256
Eportfolios (40 members)
https://plus.google.com/u/0/communities/115269504984661775868
Computer Science Education (33 members)
https://plus.google.com/u/0/communities/115153713433668200536
Engineering Training and Education (24 members)
https://plus.google.com/u/0/communities/111157504937803017265
Engineering Educators (18 members)
https://plus.google.com/u/0/communities/107268234212535588765
Eportfolio: The fundamentals (16 members)
https://plus.google.com/u/0/communities/108377089913226761465
Original List of Educational Google+ Communities from January, 2013
[The number of members is from January]
Education Revolution (3493 members)
https://plus.google.com/communities/104214480154015052148
Google Apps for Education (1836 members)
https://plus.google.com/communities/101802680117484972712
Libraries and Librarians (1203 members)
https://plus.google.com/communities/107650174557257755836
Education (771 members)
https://plus.google.com/communities/108308156289773545145
MOOC (765 members)
https://plus.google.com/communities/117130483000476703182
Higher Education (703 mmbers)
https://plus.google.com/communities/109197000367826307040
School Technology Leadership (632 members)
https://plus.google.com/communities/102874431495428943182
E-Learning and Digital Cultures MOOC (493 members)
https://plus.google.com/communities/116967860906905648378
eLearning Development (476 members)
https://plus.google.com/communities/102138711087401569660
Moodle (474 members)
https://plus.google.com/communities/106727905874888429913
Instructional Design & E-Learning (454 members)
https://plus.google.com/communities/115261781035799088895
Deep Learning (431 members)
https://plus.google.com/communities/112866381580457264725
Educational Technology (396 members)
https://plus.google.com/communities/118155617276327496151
Play Based Learning (352 members)
https://plus.google.com/communities/116229270390659374688
Massive Open Online Courses (344 members)
https://plus.google.com/communities/105926059754841899661
Tech in Edu (335 members)
https://plus.google.com/communities/107482442125144594872
Connected Learning (328 members)
https://plus.google.com/communities/113655426574061601680
Learning in Organizations (315 members)
https://plus.google.com/communities/108199456427729473693
Educators on Google+ (282 members)
https://plus.google.com/communities/100342834366095345013
Using IOS Devices in Education (265 members)
https://plus.google.com/communities/104443895202821212385
Code4Lib (238 members)
https://plus.google.com/communities/114587042187424680647
Global Education Conference (234 members)
https://plus.google.com/communities/113486387602008324050
Technology & Innovation in Education (221 members)
https://plus.google.com/communities/117631661795101086867
Inquiry-Based Learning in Mathematics (197 members)
https://plus.google.com/communities/107762594334871181831
Mathematics Education (191 members)
https://plus.google.com/communities/106364254296651187923
EdReach Network (171 members)
https://plus.google.com/communities/108928019712291099224
K-12 Education (169 members)
https://plus.google.com/communities/117583754165193896165
Online Learning (157 members)
https://plus.google.com/communities/107062761204073481218
Parent Teacher Play (149 members)
https://plus.google.com/communities/108685812453178276517
MOOC MOOC (141 members)
https://plus.google.com/communities/104740130076825758720
Digital Education (124 members)
https://plus.google.com/communities/114620229687393085644
Appademics (123 members)
https://plus.google.com/communities/115982721809744443471
Teach Preschool (105 members)
https://plus.google.com/communities/112513715918970198662
HigherEd (94 members)
https://plus.google.com/communities/115644422935294078103
Mobile Learning (87 members)
https://plus.google.com/communities/111477232632795074486
Learning Fast in the Age of MOOCs (81 members)
https://plus.google.com/communities/107901009078869528613
Learning to Code (74 members)
https://plus.google.com/communities/116128404191074510837
OLDS MOOC (72 members)
https://plus.google.com/communities/114085469619615490101
School Psychology (56 members)
https://plus.google.com/communities/110569049731019319789
Educational Technology (49 members)
https://plus.google.com/communities/112629018730625565790
US History Teachers (46 members)
https://plus.google.com/communities/108806596170395806531
Geography Teachers (40 members)
https://plus.google.com/communities/105749379394936886921
School Library Media Specialists (33 members)
https://plus.google.com/communities/117972083606648197914
History & Social Science Teachers (16 members)
https://plus.google.com/u/0/communities/102654955447474099260
Philosophy of Education (8 members)
https://plus.google.com/communities/104393533655199444132
Faculty developer. Interests: developing educational technology; faculty & student development; learning sciences & psychology.
EdTechDev - Doug Holton 
Thanks for taking me sideways, I wanted to be productive today but your website burned up most of my morning. Great reading. Thanks again.
Melissa McClatchy: mentioned this in If you are trying to find other Google+ communities for you or your teachers to join, here’s a list of 80+ education related communities I’ve found. Let me know if you know of others and I’ll add them to the google doc: https://docs.google.com/document/d/1hUCtyvzD_Z6EUWwVeyH7GSr…. via plus.google.com
Professional Development for VocED Trainers: mentioned this in Trainer/Teacher Google plus communities
https://edtechdev.wordpress.com/2013/11/15/80-educational-google-communities/. via plus.google.com
Andoni Sanz: mentioned this in plus.google.com/ AndoniSanzTeacher/posts/cJEwdcEjycF. via plus.google.com