Smart Kit (no affiliation with SMART) offers a large collection of games, puzzles, and riddles for students of all ages. The content of the collection ranges from simple drilling-style games to challenging word puzzles. There are sixteen categories of games offered by Smart Kit. The categories of most interest to educators are probably the math puzzles and word puzzles categories.

Applications for Education
In addition to the online games, Smart Kit offers a selection of games and puzzles that can be printed for offline use. The printables collection could make Smart Kit a good resource for teachers whose students have limited access to the computers in their classrooms.

Here are some related items that may be of interest to you:
HeyZap – Strategy Games for Your Class Website
ABCya – Fun, Educational Games for K-5
Starfall – Interactive Reading Lessons and Games