Asus, Acer, and MSI all make good netbooks. You may just want to try narrowing your options down (websites like Newegg, eBay, and even Best Buy) by comparing prices, looking at models, etc. Then do research on models you are interested in.
I just bought an MSI Wind for $340 on eBay. It's the 6-cell battery model (U100), and that was a pretty good price. There's also the newer U120, which is basically just a face lift of the U100 (but you can't upgrade the RAM).
Your criteria gives you tons of options...I wanted to make a Hackintosh netbook, so the MSI Wind was the best choice for me.