Halo: My household expenses for last year were paid for by Halo. 
Eve Online: Spent a lot of money on this with two subscriptions and it’s worth it, my favorite game ever.
Rainbow Six Vegas 1 and 2: so much that I have bought them a couple of times after being robbed.
Civilization series all of them.
Mirror’s Edge: This game is just super-dope.
Force Unleashed: This game is just fun.
Quake except 4.
Yes, I’ve logged over 4000 games of Halo 3. I play the shit out of that game and love it. I didn’t bring it up before because I won it in an online tournament, so it’s not technically a use of my “gaming dollar”.
Yeah, if we count games that you get for free, there isn’t just the rogue-likes, but The Ur-Quan Masters also deserves a mention.
Sim City (original)
Spaceward Ho!
Intelligent Cube (which is the only PS game that still gets replay on my PS3)
How about Stronghold (the original one), and also Crusader? Tropico was time consuming as well.
Rome: Total War. The game itself was genius in of itself, turn-based nation building seamlessly combined with gritty battle tactics. Modded, though, it takes on a whole new life. I haven’t seen a better RTS game, before or since.
Command and Conquer: Red Alert. Sparked my love of RTS’s in the first place.
Oblivion. I’ve probably gotten more hours out of this game than any I can think of…except maybe Rome.
Sonic the Hedgehog. Retro! Sparked my enthusiasm for games full stop. “SE-GA!”
Mercs. Another retro one, one of the few shooters I’ve ever engaged with.
Age of Empires II. Another quality RTS game.
The Sims. Shut up.
Metal Gear Solid. The game that MGS2, 3, and 4 wanted to be.
I have to disagree with the last bit. MGS was a great game, but seemed too…fantastic for the setting. Its hard to put my finger on, but it lacked plausibility, which I think is a factor for a game with its setting. MGS3, OTOH, was a gritty, realistic game and I ‘bought’ the story. I think the difference between the two was that MGS1 seemed like a stretch story-wise, while MGS3 was pretty believable. As for MGS2… Well, the scenes before the last fight kind blew it for me. I was disappointed, to say the least.
As for The Sims, there’s nothing to be ashamed of! A lot of little girls like to play dolls! (Seriously, though, that game nearly eliminates the need for a real life. I don’t need real people to be my friends, I’ll just make Sims of them and make them like me!)
I like the ‘twenty minutes into the future’ setting of MGS, tech that seems plausible if not wholly realistic. You may be right in the case of 3, I did enjoy the Cold War business going on there. 2 and 4 though…
The Sims I only play to, er, torment them! Yeah, manly violence and stuff. Not raising families and simulating relationships. Nope.
The Orange Box – the sheer number of play hours I put into Team Fortress 2 and the marvelous experience of Portal both make up for my losing interest in Half-Life 2 (which I’ll pick back up eventually, it seemed like an excellent game, I just tend to lose track of games sometimes).
World of Warcraft - I became addicted, which is bad, but this is the only game I’ve been paid to play (sold my account for $500 after a year, which covered all of the subscription fees and costs and then some). Plus I played about a bajillion hours and had a lot of fun, too.
Ancient Anguish – A free MUD, but I donated $10 at some point – over 150 days of active playtime. Granted it’s taken me about 12 years to rack that up!
All of the RTS games I bought at bargain prices and played the heck out of – Age of Empires 1 and 2 (3 I bought full price), Starcraft, the Kohan games, Civ II, Alpha Centauri, etc.
Diablo II/ LoD are on top of my list, if we exclude free games (otherwise it’s NetHack by a LOT).
Civ II is second, with Starcraft/Broodwar third.
On second thought, there’s one that I haven’t played as much as the above three that I may have gotten more enjoyment out of - OOTP (Out of the Park Baseball). The two online leagues I’m in have given me tons of enjoyment. Probably still second to Diablo II, though.
For me, it’s probably Half-Life I, as I spent countless hours on Counter-Strike and Team Fortress Classic. For the latter, I became disturbingly good at rocket jumping and concussion jumping (with a Medic), feats that when I started seemed like complete magic. Damn, it was fun zipping around the map, infecting people, and then blasting off into space before they even get the chance to turn their mini-gun on you…
Unfortunately, my comp can’t handle Half-Life II, though in terms of my life as a whole, that’s probably a good thing. 
Half Life, Counter Strike and Condition Zero. I started off playing Half Life as my first PC FPS and spent days trying to beat that game. Then I joined all my friends who were playing counter strike. That entertained me for years. Now I play Condition Zero. I have both the older and new version but choose Condition Zero because of the Clanless Fraggers server. It’s a group of people that don’t whine and bitch all the time (very hard to find).
I tend to do things like not being able to find a game I want to play at the rental place so I go out and throw away $50 on it and end up hating it.
So I’m hoping that my smartest video game dollar is the $15 a month I just agreed to pay GameFly so I don’t do that shit anymore.
Any other GameFly’ers? If so, what’s the poop? Does it work for you?
Dungeon Keeper II is one of my favorite games and it’s one of three games currently installed on my computer. I would find it was late at night and realize that the neighbors might not appreciate the Dungeon Mistress moaning at 1:00 AM. I love the Jackpot Winner animation. It’s the only game I know that at midnight asks if you ever sleep, as a reminder you might want to sleep before work.
The Oblivion “Game of the Year Edition” I bought for $20 this spring is one of my best buys in a long time.
World of Warcraft. It’s pretty much eaten up my available free time since November 2006, and my interest has shown no signs of flagging. At $15/month per account (I have three, the spousse has one) it’s a great value.
WoW has actually saved me money. I pay my $15/month, and sit at home playing instead of going out and spending money on frivolous stuff
Unreal Tournament. I understand fps games are not everyone’s cup of tea, but I played the original for 5 years, hard core, daily, hours at a time until my hand cramped up.
Runner up, Civilization. The entire series is my drug, but the best value was the original. Hundreds and hundreds of hours easy. Cost me just under $30.
Yeah, you and me both. I used to go shopping when I got bored–now I play WoW. Saved a ton of money–so much that I didn’t even feel guilty when I bought my main a Spectral Tiger.
Ico. It’s not my favouritest game evar, but it’s the only one I’d gladly pay another $50 for.
The Sims (and expansion packs). It’s pretty much the only game I play. I do enjoy puzzle games like Myst but there’s not a lot of replay value in them. Well, there’s a sort of replay value. Every few years or so. If I can find my old notes.