Currently, Terraria tops that list easily.
414 hours, 10 bucks on launch (bought the 4-pack for 40, and was reimbursed).
And the game has just reached its one year anniversary.
Yeah. I kinda like it.
Followed by Borderlands, UT2004 (re-purchased since my CD collection was stolen), X-COM 1 through 3, Plants Vs Zombies, and then a smattering of games that took a while to beat the first time, but I haven't really replayed.
For my ALL-TIME best (not just in the last 5 years): Either Age of Empires 2, Master of Orion 2, or Diablo 2. I've also beaten Super Metroid and the first 5 Mega Man X games an unhealthy number of times.