Confused about the huge assortment of graphics cards available, their power use, their performance and other details? Hopefully, this page will clear things up a bit by pointing to the right places to understand more.
The two main vendors of gaming graphics cards are AMD (formerly ATI) and Nvidia. They produce Radeon and Geforce branded graphics cards respectively, and these are resold by a number of other vendors (Sapphire, Evga, HIS, Asus, XFX, etc.) who customise the packaging, cooler, support and sometimes the speeds of the cards. Except for the versions with altered clockspeeds, all cards of the same name (e.g. Radeon 5870 or Geforce GTX 470) should perform the same, and so the choice of which sub-vendor is not that important compared to the choice of card.
Graphics cards have a number of key specs that determine performance, though these are only useful to compare within a family of graphics cards rather than between generations or vendors, because the internal architecture varies so much.
Clockspeed - Shader count - Memory bus - Memory type - Memory speed
PassMark Software - Video Card Benchmarks will give you overall performance benchmarks on pretty much any video card you can think of. What it will not do is go into details about performance - it is a general indicator. You will probably be wanting to go straight to the high end GPUs here. Or, you can search for a GPU here.
Tom's Hardware Monthly Gaming GPU Buyers' Guide This is a monthly review of the best graphics cards in given price ranges (admittedly US dollars, but applicable elsewhere), and also a hierarchy chart of desktop graphics cards providing a rough idea of where they stand relative to each other.
Make sure you have an adequate power supply if you're building your own computer - not doing so could have some undesirable side effects. You can calculate approximately how powerful PSU you will need by using the Corsair PSU calculator here.
Some Graphics Cards require power directly from the PSU (not through the Motherboard). If this is the case, you will need to make sure your PSU can support the connector required by the graphics card.
Graphics Cards come in 3 types:
Before buying a Graphics Card, make sure you are buying the correct one! You can check with your PC supplier to find out which one you have. If you are buying a new PC, then the card and motherboard will almost certainly be PCI-E as the other two have been obsolete for a while now.