Just a warning about ATI cards (and yes I do have one myself). There have been numerous problems reported with the latest Catalyst drivers, to the extent that many people revert back to older ones, this seems to be a perennial problem too.
Also, be warned, some more modern games and sims do not display well on ATI cards, as a result of the driver difficulties, a prominent example of this being the FPS combat sim, Armed Assault (aka ARMA, the Op Flashpoint semi-official sequel). This game features dramatic lighting and lens flare effects which, to be honest, make the game nearly unplayable on ATI cards, so if that's a potential piece of software you want to run, I'd very seriously recommend avoiding ATI. Take a look on the ARMA (Bohemia Interactive) forums if you want more info on this. I know NVidia cards are not without issues too, but I'm just commenting on what has been a real pain in the ass for me, having an ATI card (I won't be buying another).
Chock