This is similar to the other "Top 3 Favourite Games of All Time" thread, but instead... list your top 10 BEST games of all time. (Not necessarily PC games, any games)
Here's my top 10.
1. Deus Ex
2. Crusader: No Remorse
3. Ecco the Dolphin
4. Operation Flashpoint
5. Outlaws
6. Half-Life
7. Wing Commander III: Heart of the Tiger
8. Super Mario Brothers 3
9. Sonic the Hedgehog 2
10. Metal Gear Solid

Even though it's hard to make the list here's my go at it:
1. Baldur's Gate (the series)
2. Planescape: Tourment
3. Fallout 1
4. Fallout 2
5. Team Fortress 2
6. The Longest Journey
7. Myst Series
8. Heroes of Might and Magic 2
9. System Shock 2
10. Commandos 1
I couldn't place Fallout 1 and 2 on the same level as I could with Baldur's Gate and to an extend Myst.

Insane thread... ;D How one can possible choose? But lets try this... Most of these games might feel little bit stupid nowadays and cannot possible compete with even that sillyest ipod game ever, but still - these was The Games that I've played.
My All Time Top-10
1) Arkanoid 2
2) Impossible Mission
3) [url=http://en.wikipedia.org/wiki/Stunts_(video_game)]Stunts[/url]
4) Dune 2
5) Dune (Yes. I also have Dune movie, Other Dune games, all the books etc... ;)
6) Syndicate
7) Gateway 1&2
8) X-Wing
9) Master of Orion 1
10) Ufo Enemy Unknown
Maybe it is just that I am over 30 by now, but I cannot find anything to play from these new games. Too many buttons, too many switch and not so much game or story...

Damn, I forgot about Monkey Island (1, 2 and 3; didn't care that much about 4), Grim Fandango, Discworld, Day of the Tentacle... oh man, there's so many of them!

1- Doom II Hell on Earth: This was my very first game and it has since left an impression on me. I love the shotgun like a brother and nothing fills my heart with more joy than gunning down a room full of enemies on ultra-violence and not lose any health.
2-Doom: Same reason as Doom II except this was more of the same great action I saw in Doom II.
3-Heretic: Considered THE Doom Clone since it was the first released game aside from Doom on the doom Engine. Guess what? The game deserves its praise because it gives the action of doom in a fantasy setting and I am a big fan of fantasy.
4-Hexen: The sequel to Heretic and has some different elements. This game retains the action of Heretic and Doom but adds puzzles to the mix and gives it an adventure/rpg feel. I consider this one of the first fps/rpg hybrids done right. Still a masterpeice and a good game in its own rights.
5-Diablo II: No game has taken as much of my life as Diablo II. I must have 2000 hours into this game simply because the gameplay is simple and never gets old. This is always fun to play with friends online and never gets old because of randomly generated dungeons.
6-Team Fortress 2: Never has an online shooter drawn me in like this game. The ease of play and great teamwork makes this game an overall great addition to any collection and makes for a great experience.
7-Quake: THE online shooter. I never played this online as much as I could have but I loved the single player to death. I got this when I was 8 or so and as you can imagine I was scared out of my mind in this game because it was so different from anything I had seen before. Great game with great memories.
8-Descent- I got this a little later than my other dos based games thanks to a pc gamer and loved it. I played it until my old laptop died (98) and then this site resparked my interest in it so I could get it again.
9-Company of Heroes: Never before has an rts grabbed my attention like this little game. Instead of the slow resource hoarding rts's like starcraft this game has a heavy emphasis on STRATEGY and unit placement and not spamming mindlessly.
10-Half-Life: The game that designed modern fps play and gave you a good group of scripted events to boot. When I beat this game I knew it was a great game and deserves the praise it gets.

My 10 ten games of all time are
1 Carriar command (atari st)
2 Civilization - series
3 Fallout 2
4 Everquest
5 Baulders Gate 1 & 2
6 Midwinter
7 Damaclos - mercenery 2 (atari st)
8 Red Alert
9 Frontier - Elite 2 (atari st)
10 Elder scrolls morrowind

1. Close Combat series
2. Fallout series
3. Blood & Magic
4. KKND Xtreme
5. Heroes II Gold
6. Undercroft
7. Settlers II Gold
8. Warcraft II + Exp.
9. Master of Magic
10. Shivers

Good topic...and tough decision! I'm gonna have trouble picking 10, much less ranking them. :)
1. Xcom : UFO Defense - I've probably invested more time playing this game repeatedly than any other game, ever. Hence, it gets the win.
2. Steel Panthers : World at War - Dated visuals, dated game code...and I still crank it up at least once a week. And there are still campaigns being made for it.
3. Half Life
4. Master of Magic - I'm still waiting for someone to release something that even compares.
5. Silent Storm
6. Elder Scrolls III : Morrowind - Remembering the sheer amount of time I poured in to this game is the sole reason I STILL haven't picked up Oblivion. :)
7. Fallout 2
8. World in Conflict - One of the best RTS games I've played in awhile, simply because it got rid of the cliche RTS crap (basebuilding, resource gathering, etc.) and focused on the point...combat.
9. Sid Meier's Pirates - Loved the original, AND the remake.
10. Deus Ex.

I would have to say, in no particular order my ten "most played classic PC games". I don't have a top 10 since it evolves constantly.
Wasteland (why has no one remade this??? it's the spiritual predecessor to Fallout)
Duke 3D
Doom II
Stunt Car Racer
Half-Life
Leisure Suit Larry Series
Command and Conquer
Maniac Mansion
Zak McKracken and the Alien Mind Benders
Myst
Fallout Series
I go to 11, must have watched too much Spinal Tap! I mean there's definately more: the Zork series, Ultimas (even Ultima Online, which i just quit a year ago after 7 years playing), Dungeon Master, and many many "modern" games. These are just the ones i have fond memories of that would be practically unplayable on current systems without tweaks (with the exceptions of maybe Myst and Half-Life)

Best: 1. KKND
2. Original War
3. Suikoden 2
4. Final Fantasy 7
5. Theme Hospital
6. Command & Conquer - Tiberian Sun
7. Mass Effect
8. Hegemonia - The Legions of Iron
9. Sword of The Stars
10. Ground Control 2

Not in any certain order.
Command & Conquer
Command & Conquer Tiberian Sun
Deus Ex
Fallout
Descent
Doom
Shenmue
Galaga
Rez
Duke Nukem 3D

in no particular order
1. tetris
2. doom ii
3. samurai shodown 2
4. tempest
5. TIE fighter
6. super mario world
7. starcraft
8. peggle
9. silent hill 2
10. portal

Top ten is SO hard.....
10. Manic Miner (old ZX Spectrum) - grandaddy of platform games, purer than Jetset Willy
9. Doom/DoomII/Ultimate Doom - lumped em in as one, extra points for the modern conversions with the updated graphics
8. Sensible Soccer - grew up with this one - the playability!!
7. Descent Series - pr'aps biased because of new play from GOG, but fantastic game series
6. Freespace Series - best space sim, bar none (well, maybe one...)
5. Oblivion - graphic and gaming rpg heaven
4. Thief series - blew me away when first came out, a whole new genre to play with!
3. Half-Life 1/2/Episodes - True gaming goodness
2. Match Point - totally from left field, this one. Old ZX Speccy Tennis simulator, of all things. I still play it on emulator now - beating the Computer in the final is a bitch.....anyone else who played this knows exactly where I'm coming from.
1. Elite - THE space sim. Played the original BBC version, played the Speccy version, and now play the PC update - Oolite. It may be simple mechanics, it may be old, but its classic and its gameplay can't be beaten.
There you go - totally subjective, but thats the point of these threads, aint it?!

ESP Ra.De.
Ikaruga is hard beyond reason, Titanion and Chorensha 68K could use some visual variety, and Touhou games kinda creep me out.
Virtua Fighter 4
I also play Last Blade 1 a lot, I respect the strategic depth of Street Fighter 2 and 3, but all those 2D fighters are hell without an arcade stick.
Hostile Waters: Antaeus Rising
Battlezone PC is also good, but I love giving orders while paused and jumping into any of my units.
Rainbow Six 3: Raven Shield
Vegas is a hell of an experience (especially in co-op), but lost a lot of Raven Shield's weapons and depth.
Phantasy Star 4
Betrayal at Krondor almost won, except I've replayed PS4 more. I played a ton of Blades of Exile back in the day, but no longer.
Freespace 2
Elite and Privateer are a good concept, Wing Commander and TIE Fighter were quite well-made, but none are remotely as accessible to players other than Air Force veterans.
Splinter Cell
The incompetence of Thief's guards can get a little silly. Metal Gear Solid is just too damn talky.
Super C
Seems to be better balanced (fairer) than other Contras and Metal Slug.
Castlevania 3
Super 4 has some rough edges, and I don't find myself going back to Rondo, SOTN, or Psychonauts as much.
Dungeon Crawl
I don't die or spring for the keyboard reference as often as in Nethack, ADOM, or IVAN.

Maybe a bit mundane, but if I could only own 10 games...
1. Ultimate DOOM
2. Fallout
3. Day of the Tentacle
4. Tyrian
5. Ultima 7 (If both is cheating then just BG)
6. Half Life
7. Planescape Torment
8. Myst
9. Daggerfall
10. Full Throttle