In no order...
The Bard's Tale I: Tales of the Unknown - I remember playing this game with my grandfather back when I was 3 or 4 years old. This and Phantasie III. Needless to say I've been a CRPG player since. I played originally on a Commodore 64, though I still have the game for the PC. I haven't played since switching to Linux though.
Phantasie III: Wrath of Nikademus - Another game I remember from way back. I much prefer the superior C64 graphics to the cruddy PC one. But, it's still fun and I've played a few times since. My own project RPG has a UI based on this, with some other elements lifted from it.
Advanced Dungeons and Dragons Forgotten Realms: Treasures of the Savage Frontier - The first CRPG I finished. I loved the more tactical combat aspects of the game, and it actually is what got me into wargames like Steel Panthers: World at War. Wargames are my second favorite genre of video game.
Wizardry VIII - The best modern RPG I have ever played, and one of the best period. I loved Wiz 6 and 7 as well; but 8 just blows them out of the water.
Ultima 6 - While Ultima 7 is said to be better, I haven't played it (I do have it though). I just love going through this game. I actually had a game where I stile everything that could be picked up or pushed, and had a 'base' in each town loaded with ill gotten gains. I also killed all the NPCs.
I still haven't beaten it because I get sidetracked and just play around for sheer enjoyment.
Ancient Domains of Mystery - My favorite of all the rogue-likes. In my copy on this computer, I have over 100 dead characters listed. I've probably run this game over 1000 times and it never gets old.
Egg's Ultima Online (EUO) - An MMORPG based loosely on U4/5. I haven't played in a long while, since I switched to Linux. But it was incredibly fun and addicting, though I never got much into the community aspect. I just soloed everything.
Might and Magic: World of Xeen - I don't consider the two separate games whole unless they're together. I've had hours upon hours of fun with this; to the point that my last party was two characters. I wanted to solo it, but certain skills require two characters to have them (mountaineering and pathfinding) and as such, a solo game is nearly impossible. I also love M&M 2 and 3, which deserve mention here as well.
Divine Divinity - I had a blast playing this for a brief time, until the disc messed up. Now I can't play it at all. I haven't played in a long time.
The Summoning - And old SSI game, with an isometric POV. Both me and my uncle spent many hours playing this. I got stuck in the teleport maze. I remember it more fondly for my uncle, who died due to complications from his diabetes, than for the game, but it is still a solid game, one that has a few elements I like well enough to use in my own dream game. The game Veil of Darkness uses the same engine, in a gothic/horror setting. It's pretty good, but much harder.
Baldur's Gate - One of the very few games I've bought twice. I wore the original discs out. I like BG2 as well, but I haven't rebought it yet(the discs on my copy are worn out there too).
honorable mention
Devil Whiskey - While not technically the best I can name, I mention this because I was on the original dev team, when it was Bard's Tale IV. I left before it became Bard's Legacy, which was later dropped due to copyright issues for just the name DW. I used to post regularly at the forums, but it wouldn't load last few times I tried to go there, so I quit bothering. I disagree with the devs promising to release the source, and then not doing so (breaking not only their word but a licensing agreement with some OS stuff they used in development). As it was the first game I had a hand (however brief) in, I'll mention it. It taught me what not to do when selling a game, and what to do; so I owe it that much.