Hey crobin, welcome to the forums.
Your Radeon 9700 Pro is built to the AGP 8X standard. Any of the boards using the Intel 865PE, 875P or E7205 (aka Granite Bay) chipset will support AGP 8X, too. They also support Dual Channel DDR memory. If you picked up two sticks of PC3500 you'll be able to take advantage of that, too.
Your best bet for a cost-effective mobo will be one using the 865PE chipset. These cost less than the 875P models while giving up little (if anything) in performance. The Asus IS-7 is getting good reviews but I'd also recommend 865PE boards from Albatron, Asus and Gigabyte. All overclock well and have the best reputations for reliability.
BHD