^^good advice. We really can't help much more other than links to best value and our own opinions based on the information you've provided since everyone's "within reason" is different.
In my opinion, within reason is a radeon 5870 and Phenom II 955 if you have the money. I prefer the reliable performance of a single card. crossfire etc is great and will perform better just not twice as much and in some games, there is little to no benefit at certain resolutions. The phenom II 965 performs better but is overpriced. The i5 and over will provide no noticeable performance advantage except in a game like Flight Simulator X.
For WOW though, I think this is a bit overkill. You'd be fine with a radeon 5770 or 5750 with a 3 core phenom II. I don't know too much about WOW, so don't quote me on it until someone backs up or refutes my claim.