I'm really surprised no one has mentioned a Tualatin compatible motherboard. Heck, if you are going to get another PIII mobo, might as well keep your upgrade path wide open.
Oldfart recommended the ASUS TUSL2-C based on the Intel 815 b-stepping chipset. In general, the benchmarks I've read but it at same or better speeds than the VIA133A chipset boards like the P3V4X. I like my P3V4X but I'm looking at replacing it with the TUSL2 so I can drop in a shiney new Celeron 1.0A Tualy and OC it to 1.3 ghz.