Well this comes down to short games because they are easy to finish:
- CoD, CoD:UO (probabaly replayed these hundreds of times, it just became a Sunday tradition)
- Hal Life 2 (this one probably comes close to 50 replays, it's just somuch fun)
- Portal (ya this one is just so short you can blast through it in half an hour, the user made map packs probably give you more game time then the original, so thank god for fans)
- Deus Ex (it would rank up much higher if it was a short game, but it's not so it barely reaches the double digits)
- Baldur's Gate(havent done many replays because it's a really really long game(unlike the new breed of RPG's), but the time I spent on it is far beyond everything else)