If it's a netbook you're after then I still recommend the HP Mini 510x family. The Mini 5102 offered build quality that was better than a lot of full-size notebooks, an 11.6" 1366x768 LED backlit screen, a six cell battery, a 7200rpm HDD and an almost full size keyboard for the same price as other vendors were offering 10" 1024x600, 4 cell and 5400rpm machines. It's replacement, the 5103, is starting at the bottom and working it's way up again, but if you see one with the 1366 screen and 6 cell battery for around your budget, grab it.
The other machine I'd keep a look out for - and brace yourself, because I almost never recommend either of these separately these days so to recommend them both at the same time is surely a sign of the apocalypse - is the
ThinkPad X120e with the AMD E350 processor. The E350 Zacate APU is supposed to compete in the $400-500 full size segment, but doesn't quite make it. It does, however, perform amazingly against Atom in the sub-$400 netbook market.