Quake III online for DC is great. I've lost countless hours of my life to that game online, as it plays like a dream, especially considering it's mostly played on 56k.
You really do need a mouse and a keyboard to play it properly, although I used to play with a mouse in one hand and a controller in the other, as it felt much more natural to me. I hate playing games with a keyboard, and you can do all the same things with a controller/mouse combo that you can using a keyboard/mouse combo. I used to be totally addicted to that game playing for several hours in one sitting.
Now, I've moved onto greater and better things: Unreal Championship on Xbox! I should crack out the Quake III sometime soon, and relive the old glory days though...