Then, for now, you DON'T want ATI on-board or as a PCI-E card for your GPU. The story might be different in a month or so (the next fglrx driver MIGHT fix most of the issues we're seeing right now...) or in about 6-12 months (they get the rest of the specs out to the Open Source community and we get things going in a timely manner...)- as it stands now, ATI is only for the brave of heart or the R600 owner...sort of...
Also worthy of note would be that you probably don't want any of the 8xxx series G80 based NVidia cards either- they're also currently problematic in their own way as the ATI driver/card situation is right now. Your best bet would be a 6 or 7 series NVidia, or the on-board GPU if you're getting one with a GMA950 or GMA 3000/X3000 or similar if your 3D needs aren't terribly stringent. In the case of the Intel support it usually just works and no special driver fetches needed as it's all Open Source to begin with.