Heh, I just started replaying KotOR today. I saw a picture of Bastila, I had to go back to her. Jennifer Hale makes every game replayable. I think good voice actors are the real selling point for me. Heck, I replayed the Legacy of Kain series several times just for the dialogue.
Speaking of memorable dialogue, has anyone noticed that every Bioware game has the line: "This place is about to come down around our ears!" I get a kick every time I hear it.
Guys, I'm worried about the KotOR 2 RP. They haven't had any progress updates in a year. We might have to send em a petition to keep chugging or something. Actually I got KotOR 2 on the xbox, so if it comes out I'd just have to pay more for the PC version. I'd really hate to support a company putting out an unfinished title twice.

For me, it's got to be the Mechwarrior/Mechcommander Series, Always have loved those games (especially Mechwarrior 4 Mercenaries)

off the top of my head:
Skies of Arcadia DC (played it twice already on the third go around)
FF Tactics (both on my ps2 AND the psp, go figure)
Xenogears (THE original....so good)
Bridge commander
MW II (IF I can get my controller/joystick to run in XP :p)
Restarting Company of Heroes as my install got messed
There are so many others I have no idea at this moment...

What is the RP exactly?

RP means RolePlay. Both first episode of Kotor were amazing speaking of RP :)

... And when speaking of KOTOR 2 RP, it's Restoration Project :D

Sweet Jesus! You're the biggest old school game lovers I have ever seen!
1. Diablo about 10 times
2. Diablo 2 - 5 times
3. Fallout 1,2 and BoS - summary 7-8 times
4. Heroes of M&M (all of it) - never ending
5. Warcrft 2 Tides of Darkness - 5 times
6. Call of Duty 2 - 3 times
7. Call of Duty 4 - 3 times
8. Far Cre - 4 times
9. Max Payne series - all the time (unfortunately first doesn't work under XP - maybe www.gog.com will solve this problem)
10. Indiana Jones and the Fate of Atlantis - 3 times
11. Dungeon Keeper series - 5 times
and many more...

Well what did you expect, a donut? :D

Funny thing) But trust me the last thing I expected to find here is a donut)

To me it's:
Serious Sam (First & Second Encounters)
Giants Citizen Kabuto
Operation Flashpoint
Fallout 1st, 2nd & 3rd
Prince of Persia Trilogy
XIII Best game ever, UBISOFT masterpiece
So, these are my favourite and never gettin' bored games.

Bejeweled Twist.
Again again & again, can't play & review any other games.
(even if Bejeweled is not your type.)

Diablo 2 has to be the game I have replayed the most. I can't even count the times I have gone back to play it.
Secret of Mana I have replayed this game several times over the years.
Dawn of War Excellent game.
Starcraft Another of my favorite games I have played time, and time again.
Chrono Trigger Another classic rpg I enjoy replaying from time to time
Fallout 3 From what I have played of it so far, this game is easily going to become one I will want to play through several times.
I have a lot of other games I like digging out and firing up, but these are my favorite's.

I actually end up replaying most of the games i play and like, so the list's a bit too long to write here. :)
But that's mostly because the games i like usually have a replay value that ranges from the huge (many cRPGs where the gaming experience actually changes quite a bit depending on the character you choose to play) to the infinite (strategy games like Civilization, or even Tetris :) ).

Oh rite I've heard that K2 was cut off... well yeah sorry bout this :P