You an play lots of simple online educational games at Tiny Tap. You can create them, too, but for that feature you have to use their iPhone/iPad app – the games are playable on computers or mobile devices.
For a monthly cost, teachers can create virtual classrooms and monitor student progress, but everything else seems to be free.
I’m adding Tiny Tap to:
The Best Collections Of Online Educational Games
The Best Websites For Creating Online Learning Games
I learned about Tiny Tap through a very good piece written by Shelly Terrell, titled 7 Ways Learners Can Improve Their English with Technology.