Naturally being a highschool kid, I know of a few games that are very addicting, mindless, and fun.
http://www.elizium.nu/scripts/lemmings/
http://novelconcepts.co.uk/FlashElementTD/
http://pixeljam.com/dinorun/
http://www.xgenstudios.com/game.php?keyword=fishy
http://www.liquidcode.org/worm.html
Another habit forming web game...
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