Trackmania Nations Forever.
Fear combat ( full version of Fear multiplayer free for all to use, recommend it really)
GTA2 ( free from R*)
Far Cry ( for free ad supported, last time I checked gamershell still hosted it though officially it's only for Yanks and Canadians, can always use a proxy to get a key I guess.
OpenTTD rocks.
Hedgewars is an open source copy more or less of worms.
I quite like R.o.s.e online even though it's a bit buggy when it comes to vista.
Frets on Fire can be very fun if you think you'd like Guitar Hero.
HL2: DM is free for both people with an nv card and an ati card, just google steam nvidia offer or ati steam offer, as is HL2: Lost coast and peggle extreme.
Used to play America's army, but didn't really like it...
That's all I can think of now, there's prolly a lot more worth mentioning.
I'll have to look into quakelive as I quite like faster paced shooters like mohaa, never tried it yet...
