But at the current time, you should get on the Newegg email list and keep an eye on slickdeals and wait for a GTX 470, GTX 560, Radeon 6870, or Radeon 5870 to get around $200 in my opinion. You can find GTX 460 1GB for $140 sometimes. I'd go with a Radeon 5850 though. I saw one for $143 a couple weeks back.
Some brands are almost always cheaper when it comes to video cards. Galaxy, MSI, Powercolor for example are usually the cheapest. On the other hand, EVGA cards are typically more/most expensive, but they also have a very good reputation for quality and support.
In theory, some of the higher priced cards may have better quality components in them (some may even be modified non-reference cards). For the most part, it's not a big deal what brand you go for in my experience. But you might get more OC headroom going for a more quality brand.