Advice on a new system

[caivoma]

I am planning on building a new decent system with a budget around 800 dollars or so. I havent been follow on the news for about 5 months so I dont really have alot of ideas for what to look for. So far, I can reuse the monitor, graphic card and hard drive. Any recommendation on everything else is really appreciate.
Thinking about getting AMD and Asus for cpu and mobo respectively.
My graphic card is ATI 9800.
Thanks