If you teach math to a far from enthusiastic audience (from time to time), you will definitely appreciate MATH PLAYGROUND. It is geared to elementary and middle school primarily. The variety of games is quite impressive for a free site.
How can these games be used to supplement a math lesson? You could create a learning center with a couple of computers in it. Students could be sent there at various times of the day, when students are pursuing varying topics of interest, to work on weak math skills in a non-traditional way. Computers have infinite patience:)
For your students who don't need additional time to master lesson objectives, they can play logic games. There is something for everyone!
ELL TEACHER PROS