Half Life series, played HL2 more times.
NFS - Most Wanted and Underground
Max Payne 1 and 2- Played the 1st one more times on my crap i810 onboard graphics card 
Call of duty(1,2,4 and 5 recently)
Doom 3
Fear
and more..but these are the topmost. Recently BAA - have completed it once but now playing it again just for fun in case something i’ve missed 
Fifa 99
Max Payne
Need For Speed - U2 and Most Wanted
Dave
Contra
Rise Of Nations
Counter Strike
Max Payne
Spartan (NES)
Call Of Duty 1
Mafia
Return to Castle Wolfenstein
GTA 3
Max Payne 2
Fight Night Round 2
Tekken 5
Syberia 1 & 2
^Bluffy nailed it! I was wondering why isn’t anyone put up RTCW so far. I so loved that game.
RTCW
AOE III
Maxpayne 1
Claw
NFS - Porsche Unleashed
I’d love to play the MGS series from the very first game without a break. If wishes could come true! 
I would love to re-visit:
Resident Evil 4
God of War
Kane and Lynch: Dead Men (I have already completed it 3 times now)
Bully
Devil May Cry 3
Mafia
GTA 3
FIFA 2003
Captain Claw (all Time Classic… loved playing it)
Unreal Tournament (HEAD-SHOTTT!!!)
That game was so tough with the Mouse + KB control scheme!!
Speaking of revisiting, I would love to play Indigo Prophecy again. There was something amazing about the atmosphere of that game.
Or you could play Heavy Rain early next year.
Amen to that. I was so disappointed when that game actually ended. It was a total movie based experience. I remember playing it late at night with lights turned off. This was one game which no one on this planet should miss, yeah even now. I just hope Heavy Rain lives up to all the expectations as it seems like a clone of this game.
@Black_Hawk: That game was made to be played on the controller. Although RE5 had properly implemented it, had RE4 had the same, things would have been so much better.
I know I have already exhausted the list of games to be re-visited, but I still have some titles which need a special mention. It’s Shadow of Rome & Shadow of Colossus on PS2. Both of which are epic in their own right. Might I dare say, Shadow of Rome’s storyline was even better than the movie Gladiator. :ashamed:
GTR 2
LFS
Titan Quest
Diablo 2
GTA Vice City
Hitman 2
Def Jam FFNY
Gran Turismo 4
Max Payne 2
PoP-WW
Yes, Shadow of Rome was great. The action parts were amazing, chopping down limbs was never so much fun, I hated the stealth part though.
NFS Porsche Unleashed (Best NFS ever)
GTA 2 (Simple and Sweet GTA)
Rise Of Nations
Halo: Combat Evolved
Mortal Kombat 4 (Goro vs. Quanchi ← This match is always hilarious)
Mentioning a 6th game:
Oni - One of my favorite games of all time. Screw M$ for buying Bungie and asking them to concentrate on Halo only. If you have played Oni you will realize that some of the sound effects are reused in Halo: Combat Evolved. I hope they’ll make Oni 2.
Ahhh. I see a lot of Caesar fans. 
I would recommend those folks to try Anno 1404 : Dawn Of Discovery if you haven’t already. Lovely game. As for my list :
Caesar III
Splinter Cell : All 4 games
GTA : All after 3
COD : All
Prince Of Persia : All
NFS Most Wanted
Brothers In Arms : All
Batman Arkham Asylum (Already finished thrice :))
and yeah…
MONKEY ISLAND - ALL !!!
Lotsa games. Don’t crib about 5 only
EDIT : Just saw prabs post I remember Oni. It was my first game with the WASD control scheme. Initially i thought of it as stupid 
But once i got used it to, it was a wonderful game.
In fact I’m going to add a couple of more ones I’ve re-played a bunch of times (I’m breaking the 5 game barrier myself ):
GTA III
Hitman: Blood Money
Have you played the Money Island Episodes Phoenix?
FALLOUT 3
GTA series
Stalker series(7 endings)