One other concern is to make sure your power supply has TWO of the PCI-Express Connector. Most modern 500W + power supplies do, but double check. The video cards everyone has mentioned will take two of them. The exception is the ATI 6850 which only takes one.

The 545 actually performs worse than the last-gen 460 I believe. I would go for either the ATI 6850 / 6870 or an Nividia 560 / 560ti if they are in your price range. The 560 ti is a very good card but is over $200. Newegg is often the best place to shop, especially since they have a lot of customer reviews you can look at. I guess you COULD also go for the older 460, but I don't think that has DX11 support.