Some great news - with the release yesterday of the SDK for HalfLife2 - Valve has also released the multiplayer deathmatch side of HL2. Woot.
I'm going to dl the dedicated server to our box shortly and get it set up.
HL1 DM was great fun & now the SDK is out too - expect to see alot of the old HL1 mods porting over, like: Sven co-op, Natural Selection, Action HL, etc.
More news: http://www.steampowered.com/index.php?area=news