|We run AMD cpu's on large number of our servers, so no need to worry about that compatibility.|
My recommendation would be to get the best CPU, motherboard, and RAM you can afford. You don't need a high-end GPU for web development like you would for gaming, so if you need to cut costs that's one item where I'd consider going with a less expensive model but one that supports DVI and 1900x1600 resolution.
For the motherboard I'd go with either Asus, or Gigabyte and for the cpu I'd go with one of the am3+ choices.
Asus Sabertooth 990FX R2.0 - $180
ASUS M5A99X EVO R2.0 AMD 990X - $130
Gigabyte GA-990FXA-UD3 990FX - $130
AMD FX-8150 8 Core Processor AM3+ - $180
There are several choices above this one which I would prefer, but they might put you over your budget.
AMD FX-9590 Eight Core AM3+ Processor - $280