Age Of Empires, Caesar III, Starcraft, Anno 1701, Diablo II..

Starcraft, followed very closely by Heroes of might and magic III.

Civilization IV.

Its between Master of Olympus Zeus & Tropico. I couldn't pick one over the other so I'll say both.

1. Deus Ex

2. Age of Empires 2

3. Civilization 3 (still my favorite Civ )

Europa Universalis II

Starcraft

I can't decide a single game so I'll mention more than just one.

Spear of Destiny was one of the first games I've ever played. I still love it. Oh, and I played Doom Shareware at practically the same time so yeah, it beats even Doom. Anyway, I've also learned to love Wolfenstein 3D, which Spear of Destiny is a prequel to, but SoD still wins.

Wolfenstein: Enemy Territory is probably one of the best multiplayer games I've ever played - everything worked. Enemy Territory: QUAKE Wars gets pretty close and with all these bad servers we have today (bad mods, maps, and all), it is actually better. Now: ETQW; before: W:ET; at best: W:ET.

Also, I've played Deus Ex quite a bit though I have yet to finish it. Still, I've loved it. It's unlucky I had to format my HDD when I was playing it and I've never managed to start it again :(

Then there's tons of classics I've pretty much missed: Blizzard's games (except for Diablo II) (also not sure if I'd consider them even close to 'best'), BioWare's games (and Baldur's Gate just doesn't work anymore: low non-changeable resolution + 22" widescreen = horrible), the Fallout series (and I'm excluding Fallout 3 here, though I have played it a bit) (by the way, I own Fallout 2 but have yet to start playing it), Paradox Games' strategy games (Europa Universalis, Hearts of Iron, Victoria - games like that)... And probably many more.

Half-life, Starcraft, Diablo, Quake, Total War
There are so many good games. I can't pick up just one.

There is just too many i was a PC gamer more then console one at some stage.

Planescape Torment, Baldur's Gate, Baldur's Gate 2, Diablo II, Warcraft 2, Age of Empires 1&2, Hearts of Iron II, Europa Universalis 2, EU:Vicotira , Max Payne, Fallout , Fallout 2, Deus Ex

just a few