Intel 865 or 875 Chipset... Nothing between them really, but 865 is cheaper.
I see a lot of recommendations for the Abit IS7 (865) and Asus P4P800 mobos around here, but don't personally have any experience with them...
Exactly how will this thing be used?
If this is just going to be a file server, it won't need that much power, so you could build very cheaply, maybe get a Athlon XP1800+ and stick it in a nice nforce2 mobo (e.g. Epox 8RDA, stick a nice big quiet cooler on it and yer laughing..
Obviously if it's going to host Multiplayer games and stuff, then you'll obviously want to consider a faster processor though.
[EDIT]
Oh yeah - what's your budget, and how much stuff do you need with it? (e.g. do you already have stuff like RAM, CDROMs, HDD, etc...)
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<font color=red>The preceding text is assembled from information stored in an unreliable organic storage medium. As such it may be innacurate, incomplete, or completely wrong</font color=red>
<P ID="edit"><FONT SIZE=-1><EM>Edited by ChipDeath on 10/08/03 01:51 PM.</EM></FONT></P>