Try an ASUS P4P800 or one of the following:
http://usa.asus.com/products/mb/mbindex.htm

roxbury wrote:

my brother bought an insignia comp from best buy last christmas. Now
unfortunately it does not come with a agp slot so we're in the market
for a new motherboard. The problem i am running into is its a pentium
4 - 478pin - 400mhz bus. I cant find a mobo to support the 400 mhz
bus, i tried one of the 533/800 ones but it didn't work. Any
suggestions???