I highly recommend the ASUS Eee PC 1005HA. It has an absolutely amazing 10.5 hour battery life and also a decent 10.1 inch screen. It has a keyboard that I found surprisingly comfortable to use, as well as a good wireless signal wherever I went as well as Bluetooth capabilities (although I don't use Bluetooth). It comes with Windows 7, too, which just came out a few months ago. I have Windows 7 on my desktop computer and it's nice to have the same operating system on my netbook.
The Eee PC 1005HA has a 250GB hard drive, which proved to be more than enough for me. It also has a 1.66GHz Intel Atom processor, which is supposed to be slightly better than the 1.6GHz processors on normal netbooks, although I can't really tell the difference. It comes with 1GB RAM, but I highly recommend you to upgrade to 2GB. It's only $42.99 for the upgrade and it noticeably makes everything run more smoothly. It's easy to install, too. The Eee PC has a back cover (like a battery cover) that you can open with a screwdriver, and you can just pop out the old RAM while sticking in the new RAM.
Out of all of the features, I found that the most outstanding one is the 10.5 hour battery life. It's so much longer than the 2-5 hour batteries of normal laptops, and makes this netbook very convenient for carrying around with me.
Amazon's reviews are also good, with 72 customers giving an average of 4 out of 5 stars. The reviews are here:
http://www.amazon.com/Seashell-1005HA-PU17-BK-10-1-Inch-Black-Netbook/product-reviews/B002P3KMXA?tag=joinlock-20
Right now, the Eee PC 1005HA is only $333.95, which is within your budget. Amazon has free shipping for everything over $25, so both the netbook and the RAM would qualify.
Good luck making your decision!