Also, depending on where you live and whether you can wait on a good deal, you can really get a lot of bang-for-your buck. At least in the US, late fall seems to be a great time to get a good deal, because computer sellers are blowing out old stock before the late-fall hardware refresh cycle. If you can wait, consider that, but don't hold yourself back if you can't. Sales typically start around a month before school starts back up, and again after thanksgiving/black Friday.
Lenovo seems to always have pretty great deals around that time, and makes excellent machines.