Educational games can be used in the classroom to build and reinforce skills. There are a lot of questionable “educational” games out there that mostly involve shooting things, but there are also some good games that can be used as rewards for completing activities or as a task during a computer station time. I found some worthwhile activities at

http://www.abcya.com/

You can choose some of the games on the homepage or select the grade level link to find more. If you provide students with a link to a worthwhile game (by bookmarking it or posting it to your website) you can avoid time being wasted on the “just for fun” games.

Update: While this site has some good learning games, there are several with questionable value unless using  touchpad or mouse is your goal. Be sure to screen the games and recommend certain ones for the students to use. You want to avoid “clicking” games that don’t require thoughtful responses or don’t reward careful answers or creativity.