If you're curious about how a specific graphics card measures up, check this link
, then click the heading "Rank (lower is better)" so that the triangle points up.
I would second a Sapphire Radeon HD 5770
(ranked 50, $99.99 after mail-in rebate) at the very least.
If you want to step it up a bit you could go with a Radeon 6850
(ranked 12th, $139.99 after mail-in rebate), or one of the nVidia cards depending on your budget.