I just got the GeForce 7800GS ($245) at Frys Electronics.
You're going to have to have a power supply with at least 350watts ($69)....that's important.
The graphics run smoothly. I was surprised how fast Civilization 4 runs with this high-end vid card.
Also, cs_militia in CS:S is absolutely gorgeous with this new card.
Of course, Oblivion is breath taking....