I just thought I would throw this out there - I'm sure it's been posted before, but I wanted to share a link to this site, Tom's Hardware: http://www.tomshardware.com/
Every two years around tax return time, I either upgrade or build a new computer. Before I buy any CPU, motherboard, or video card, I go to this site. Not only do they have reviews of just about any computer part you could think of (in said categories, and others), but they have these awesome articles wherein they break a product down against its competitor, by price point.
So for instance, you can find a comparison of Radeon vs. GeForce video cards, for under $100.00, $100.00 - $150.00, etc. They benchmark the products on games that really put the cards through the paces, and let you know the results.
Personally I'm a dedicated Nvidia fan for my graphics card, but I did find myself buy an AMD Radeon card last year because for the price range I was looking for (at the time) Nvidia just didn't have anything that could touch was AMD had available.