The Shuttle MN31N motherboard is a good one for that. It is microATX form factor, and has built in GeForce4MX graphics. It is an Athlon motherboard and takes up to the fastest Athlon XP chips. The chipset is the nVidia nForce2 with the 6 channel sound, integrated LAN, USB2, and FireWire. It's a pretty sweet board for it's size and price: $85.
I bought one a couple months back when building a small form factor PC for my cousin. It a nice unit. I don't have anything bad to say about it.
Also, if you want a smaller board and a cool looking case, check out Shuttle's XPC's. They've got flexATX motherboards in them, and there is a model equivalent to the MN31N, but I can't think of the model number right now.