I think your best bang for your buck may be an iMac. Granted, you won't be able to upgrade the video card, but if you're on a budget...you can't have everything. From what I understand, most PC games run just as good running Bootcamp.
Of course you could look at an older G5 Tower...you'd have the flexibility, but the new games will be optimized for Intel chips.
Of course you could look at an older G5 Tower...you'd have the flexibility, but the new games will be optimized for Intel chips.