I have 10 games that I've played extremely exhaustively, can't really decide which one I played most, but here's a rough list in no particular order:

1.) World of Warcraft - a full two years, daily, consistently.. 10 hours a day?
2.) Starcraft - i was a battle.net tournament guy for my entire high school, and I'm still playing this thing sometimes these days.
3.) Civilization 4 - i bought three copies of this game (excluding expansions).
4.) Medieval 2: Total War - i've won all the campaigns of all the nations.. any idea how long that takes?
5.) Gran Turismo 3 - all the cars, exhaustively abused..
6.) Tekken 3 - nobody can beat my Lei Wulong now. nobody.
7.) Diablo 2 - i have six level 99s.
8.) Warcraft 3 - me and my friends are still playing Dota twice a week, and we've been doing this ever since version 1.
9.) The Sims - the original sims actually awakened my desire to be an architect.
10.) Final Fantasy 7 - i played it through 12 times. in the process, i had a single save file with every item, materia, weapon, and armor in game. 

cmon i know someone out there does this same thing like me :P

you are a killer

my most played video game is War3 during my University studies

but compared to you, it looks like nothing ...

I recnelty started replayed it : i love footy  !!!

My top played games (probably 500+ hrs each) are:

1. Halo 2--Spent at least a year playing the shit out of this game

2. Guitar Hero 2 & 3--up until a couple of months ago i played both of these games with my friends constently for about 2 years.

3. Halo 3--got almost 3k matches in plus about 10 campaign run throughs and many hours of dicking around in forge.

Medium played games (around 100-200 hrs each) are:

1. Rock band 1 & 2--i played both of these games alot

2. Rollercoaster Tycoon 1 & 2--Back before i had a 360 i played both these games all the time.

3. Runescape--every once in a while i still play runescape.  had one free account (which got hacked and stolen) and my current account, both which are lvl 60+

Other games (around 75 hours each)

1. Fallout 3

2. Fable

3. Halo

4. Forza & Forza 2

5. Guitar Hero World Tour

And i'm probably forgetting a couple of games...

500 hours huh.. hmm..

i think i put in at least 3000 hours on WoW alone. starcraft maybe even more (you won't believe how much i played that damn thing). warcraft 3, tekken 3, gt3, probably around 2000 hours. the others, i can't give a useful count :P

The one game i've played to death would probably be runescape. I retired in the top 500 :p i'm probably somewhere in the 1300s-1500s by now though. One can't compete with those who have no life on there.

hehhe and here i was thinking ive been spending too much time with Oblivion.

I'm at 80 hours and ive only just started the main quest. I think ill probably end up with about 160 hours at most. And that would probably be the longest ive ever played a single game.

GTA San Andreas would probably be second with about 120 hours and 3 playthroughs.

i was like you until i got a girlfriend, and a job. i barely get 40 hours of gamin a week

Do you mean you've put 2000 hours into GT3 alone? or 2000 with all three of those games combined?

I played Super Smash Bros. Brawl about 200 hours and Morrowind about 150 hours but that's nothing compared to you O_o