Well here are couple too look at.
The Dell Online Store: Build Your System
The Dell Online Store: Build Your System
The only difference between these two computers as far as I know are that one is Windows 7 and the other is Windows 8. I prefer 7 but both are good. You might check them a bit more closely, these both start at $600, but with all the add on's you'll want to get (warranty's and such) you're probably looking at a $750-$1000 dollar machine. These both have Intel i5 processors, which is what my laptop has, = 3.20 ghtz so it's goes at a pretty good clip, I think. There is a more expensive dell machine that has Intel i7 which is = to 3.90 ghtz at tops, but it also starts at like $800 which to me is pretty steep price + warranty's.
edit
The links I added are sorta defunct, so just go to here; Desktop Computers & All-In-One Computers and on the side of the page there should be something called processors, check the box next too intel i5 and the first two things that come up should be the ones that the links take you to.
I'll look at what Best Buy has and let you know what I find. BTW what day's your Birthday? You said that was coming up soon.