Something with a SIS chipset, preferrably sis746. Take a look at the ecs k7s6a for example. It is very cheap and stable, and the performance is quite good too.
K7S5A hits the mark, for cheap but workable. Note they practically put insulation on the Sis 735 chip... but a bit of "goo remover" and some AS3 fixes that problem in 10 mins. Not had any other problems, even with the OC Bios.