I'd like to add to my previous post (of BG2 and Act Of War):
Disciples 2. I just cant stop. You can read my Disciples 3 thread to find out why.
Also: Test Drive Unlimited. The very best freeform game and the very best racing sim I have played.
As popular as Gran Turismo and the others are, they just dont have the same fun factor as TDU. If they could make a Freelancer mod or a sequel that had the same features (purchase multiple homes and store all your cool rides) we would have one awesome game.
Also on my personal list: KOTOR 1 and 2. Despite there are few side quests and its the exact same story each time and both games have several flaws, I keep playing them. Each of them at least once a year, sometimes more. The good far outshines the bad.
Morrowind and Oblivion: Again, each is flawed but I keep going back to see all the mods I downloaded and marvel at how rich the world is.
Heroes of Might & Magic 3 and maybe 2: Anybody who doesnt know why obviously hasnt played them, and is seriously missing out.
Master of Orion 2: Same thing. You have to experience it yourself. I cant say enough good things about it.
Also by Microprose was the good version of MTG. It has not since been duplicated. Too bad it has serious compatibility issues with anything after Win98.
Duke3D. I got the win32 version and it ROCKS!! Same with Doom95. Simple yet addictive, good gameplay.
For the same reason I like to go back to Serious Sam 1st and 2nd at least once a year. They got back to basics and its fun.