Any P4 board with an AGP slot is at least AGP 4x or 8X and 8x cards can work in 4x so basically any AGP card is fine. Radeon 9600Pro or XT is a good deal. Check NewEgg for good prices. Likely they are around $100 and $120 respectively, but I'm too lasy to look right now for you.
AMD Phenom II x4 945 3Ghz | ASUS M4A77TD | 2X WD 1TB SATA 2 hard drive | 2x2GB Corsair XMS3 | nVidia GeForce 8800 GTS | ATI TV Wonder Theater Pro 550 | Antec P-160 case | Antec 650w Earth Watts | LG Blu-ray Super Drive | LG DVD RW | Windows 7 Pro