What's the oldest game you still play regularly?

I bought Call of Duty United Offensive the day it came out and I still play almost daily 5 years later.What's the oldest game you still play regularly?
Not regularly, but I've started playing the original Rainbow Six again.What's the oldest game you still play regularly?
On PC, still a bit of Dungeon Keeper every now and then.
Baldur's Gate 1%262 almost on a yearly basis ifnot shy by a month.
Age of Empires and Red Alert. Those two never get old.
X-Com UFO Defense.
Starcraft is always a good time.
Doom. Never gets old.
I play fan made missions for Thief. It has the largest, most faithful community than any other old game has ever had. You don't see any other game that is nearly 10 years old where a large community is still making new content for and still playing.
ill second the original rainbow six ;P
Doom.
I play Doom II and Ultima VII once in every couple years.
Fallout 2AoEUrvan Assault (I only have the demo for it, it came with my AoE, I've searched everywhere for it :()
I still play Rome Total War/Medieval 2 Total War all the time.
That would be the classic ''Deus Ex''. Great game.
splinter cell choas theory. its nearly 5 years
I agree with Anna (DEUS EX)!
Diablo 2
Fallout 1,2; X-Com UFO Defence, Police Quest (1-4)
Counter Strike: Source. Although I finished Deus Ex just a few months ago.