1.Prince of Persia (SoT+WW)
2.Kingdom Hearts
3.Terranigma
4.(lol) Alundra
5.(lulz) Beyond Good and Evil
Those are the 3 ...errr 4 games, wait: 5 games I would replayreplayreplay and never get tired of it. So I call them my favourites.
Honorable mentions:
GoW(lulz)
Zelda. OoT
Conker's Bad Furday
DonKey Kong Country 2
Illusion of Time
Soul Blazor
Metal Gear Solid
Metal Gear Solid 2: Substance
Portal
Half Life
Parasite Eve
Loom
The Longes Journey
Splinter Cell: Chaos Theory
Psychonauts
Penumbra Trilogy
Afraid of Monsters: Director's Cut
Max Payne (Would be my number 6 8( )
American Mcgee's Alice( Would be 7)
Sanitarium
Silent Hill Series
Devil May Cry 1+3
Second Sight
Postal 2
Current Favourite: OUTCAST AND CRYOSTASIS FUCK YEAH

I never posted here?! Strange..
I might have to stick to PC gaming, as finding a top three just for one platform is going to be hard enough.
1. Vampire: Bloodlines
2. Fallout series
3. Call of Duty series
No, see. I feel bad, now. So many more great games out there.. Deus Ex, Civilization, Total War: Medieval 2, Diablo, Torchlight, the 'Crafts, Dungeon Keeper 2, Morrowind, Beyond Good and Evil, Psychonauts.. *head explodes*

1.KotOR series- The sith lords gets better every time i play it and its to hard to choose between the two.
2.Total Annihilation- The first rts i ever played and still the best and it was also the first pc game i recall playing.
3.Orange Box- Every game is excellent and ive probably spent more time playing tf2 than any other game.
Honorable mention.
Planescape Torment
Deus Ex
System Shock 1&2
Starcraft
Half Life 1
Unreal Tournament 99
Mass Effect

1. System Shock 1 -- hands down the BEST of the whole franchise. Nothing beats jumping into C-space to work out some interesting puzzles to affect the real world, accidentally setting off the station's laser to hit the Earth, and developing a strong need to take out the antagonist. Shodan was simply at her best in this one. Since this game, I haven't found a single survival-horror game in the same genre that even approaches the originality of the original SS. Oh, and don't forget to salt the fries!
2. Half-Life. Best darn story-based FPS I've ever played (next closest to this is Unreal 2). I might have put SS2 here, but you can't use /half/ a game, can you? I found that after you leave the Von Braun in SS2 the game was reduced to nothing more than an FPS with platforming involved. Best part of HL? The HEV suit! "Minor fractures detected -- morphine administered." Oh, and Rocket Crowbar, simply because of how hilarious the mod was. =o)
3. Command & Conquer: Red Alert. This was /the/ RTS at the time -- I still remember reinstalling and swapping disks around like crazy so I could play multiplayer games with friends over our LAN when it came out. "Hitler... ...is out of the vey... Sooner or later... time vill tell."
Best game I've played to date: Fallout 3. I just can't stop playing this one despite the crashes. And while I've beaten the game and two of the DLCs, I just keep coming back for more! SO MUCH to do in here! I suppose it doesn't help that Liam Neeson is your Dad in the game... =op

1: Fallout 3
2: Doom (all of them!)
3: Portal

1. Thief series
2. The Elder Scrolls series
3. Fallout series
It's simply impossible to name only three titles, there's a lot more than that. ;)

1. Descent 1 (By far the best of the series ;)
2. Need For Speed: Porsche Unleashed
3. Homeworld (The original, although Cataclysm was fun too, and I haven't played 2)
If I just had those three games I would pretty much be happy. I've beaten Descent only once though I've been playing it off and on for about 10 years, I've beaten NFSPU about 7 or 8 times, and I've beaten Homeworld probably 4 or 5 times. And still every time I play them, I love 'em just as much as I did when I first played them! :)
Now non PC would be:
1. Contra [NES] (Still can't beat the **** thing! lol)
2. Super Mario Bros. 3 [NES] (And can't beat this one either lol!!)
3. Super Smash Bros. Brawl [Wii]

Panzer General
Never Winter Nights - Origonal and all add ons / mods
Lineage II - Chronicle 2

1/2. Monkey Island 1/2 - not sure which would be the top spot. They nailed everything for me which up to that point I didn't realize I could even appreciate much in games, such as the musical direction and overall feel/atmosphere. They are one of the prime examples why Roger Ebert is wrong in the games as art debate in my opinion.
3. Probably Psychonauts. I missed it when it first came out and picked it up a few years later, but I've replayed it multiple times since and I have to consider it one of my favourite games. Tim Schafer is so dreamy.
These three are the most instantly memorable gaming experiences, but I can easily think of a dozen more which I'd also want to consider part of the best games I've played. I find it too hard to compare games of different genres to be at all final about what games I'd consider my all time favourites.

Planescape: Torment
Best RPG made. Like a good book.
Baldur's Gate 1
Technically not as good as 2, but this came first and the feel of the game is better for me.
Jagged Alliance 2
Humor, the best combat system made, RPG elements... takes some learning but very rewarding.
Something like that.
Honorable mentions: Ultima Online, Might and Magic VII, Heroes of Might and Magic II & III, Caesar 3, Civilization series, Shogun: Total War, C&C: Red Alert, Fallout... and so on and so on.

Baldur's Gate 2
Final Fantasy 7
SSX Tricky
Honourable mentions- Ultima Online, BG1, Neverwinter Nights 1, Outcast

The Last Ninja series
Jagged Alliance series
Ultima series, or Dune 2, or System Shocks... don't know. ;)
[edit]
oh, the Crusader's of course..
[/edit]

1.FF9
2.MGS4
3. Fallout 3

This question is almost impossible to answer. =)
1) Wasteland/Fallout series
2) Thief series
3) System Shock series
Kind of a cheap way to answer, but seriously, all these games can be tied for number 1 in my book.

For me :
1°) X-wing (the first game) The possibility to move in ship is very exciting !!! And video when your battleship is ready are too very exciting !!! I linke !!! If GOG will have it, i am ready to pay 15$ if i can play with this game with my win7 64bits !!!
2°) Doom
3°) Settlers 2