In order of most to least of the ones I've wasted significant amounts of time on:
Tetris (including the version that is supported on a TI 85 graphing calculator- it was the only thing keeping me awake in calculus)
FreeCell- the windows version with only 1 undo- my record is 42 games STRAIGHT winning streak
Dark Castles- the old Mac game. Love that fucking game!!!
And this one...
Check out my new gameplay!
That game roxors. Side scrolling cheesiness FTW~~~