Quake 2 - This was my first time playing a FPS online or with a mouse and it will always hold a special place.

Jedi Knight II - I have always been a star wars fan and this game provided the best star wars experience I ever had. The Lightsaber duels were the bomb.

BF1942 - When I heard the scale of this game I had to check it out for myself. I downloaded the multiplayer demo and boy that demo sucked up many hours of my life. The freedom of your role was so great.

CPM - I was messing with this mod for a while but then I heard a big tdm tournament (WANsanity) was coming up. So I got my q2 clan and switched it to CPM and began to have the most fun (competitivly) I ever had.

ET - I heard there was a FREE stand alone multiplayer RTCW expansion and I got it right away. This game was the most solid "out of the box?" multiplayer game to date.

Those are the ones that come to my mind right now.

How about you?