256MB AGPx8 NVidia Inno3D GeForce 7300GT DDR2 128-Bit DVI TV-out VISTA READY

If you are stuck with an AGP mobo and cannot really justify PCIe then this is the card that will give you the speed you need to cope with Vista. And it comes at a sensible price (well - from Amazon, anyway).
This is not really a 7300 card at all; it uses the 7600 architecture and offers probably the most bang per buck of all the cards in its range. Vista gives it a score of 4.3 for graphics and 4.5 for gaming (out of a possible 5.9). You will need a PSU with a capacity of 400W+; and don't forget that it has a power socket on the end of the card (takes a standard IDE device power plug) otherwise you will be staring at a blank screen and scratching your head for a few minutes...