Right now, NVIDIA 6100 & 6150 are the best, most performing onboard graphics out there, however keep in mind, that onboard gfx is made just to "run" the OS perfectly, not to play games, u know, this is something useful in offices etc, where a separate graphics card is at all not needed
Intel is about to release there GMA X3000 & GMA 3000 (for office) onboard graphics solutions, which are perfect to run Windows vista, they are also direct10 compliant, with just a driver update, they are cheap, but not meant for gaming
right now, if u want to buy get a NVIDIA geforce 61x0 chipset, else wait a while for a much efficient GMA X3000