A lot of people have been buying the ECS K7S5A (SIS 735 chipset) DDR board due to its low $60 - $65 price. It also has SDRAM slots in case you don't want to buy the DDR RAM for now. And most come with an onboard network card built in (I'm not sure about the fit with the RF shield plate on the back of the case). Let it be known that I have no affiliations with ECS.
This board is said to have great performance, is very stable, and of course the low price. ECS was reportedly the #2 seller of motherboards in the world (ASUS was #1) last year. The only shortcoming is that this board does not have much in the way of overclocking features (Larry should like this one!).
I'm very tempted to get one - my empty Antec SX830 case is dying for company.