I purchased and Acer Aspire One (WinXP version) from MicroCenter a few weeks back on sale for $350; It is a pretty decent computer as-is, but I went ahead and upgraded it to 1.5GB (max due to 512MB being hard-soldered to the board) from the standard 1GB.
There are other modifications available for this is system if you are adept with a soldering iron- such as installing an internal micro Bluetooth receiver. Today I read that tnkgrl has been able to install a mini-PCIe and SIM connector to allow the addition of a 3G wireless card.
I am not sure if this is something I would attempt (unless I get a good soldering iron), but it is nice to know that it can be done! :o)