What video card should I buy?

If you do not care about 3d performance, this question is a rather easy one. In Windows, the answer hardly matters. In Linux, it would be best either to buy a Radeon or use Intel onboard video.

If you care about 3d, then your options are narrow. The only two companies that make competitive 3d cards at the moment are nvidia and ATI. This decision used to be an easy one until the last year, where several new developments have occurred: AMD/ATI has released very good hardware documentation on their current cards, and has also updated their binary drivers to use the same core code as their Windows drivers. nvidia continues to provide fast 3d binary drivers for Linux, but on GF8 series and higher cards, 2d acceleration is known to be nonexistent or slow for many users. Worse, nvidia is probably one of the companies most hostile to open driver development --- even documentation for trivial devices such as ethernet chipsets is unavailable.

ATI/AMD's decision to release specs on their hardware and the recent vast improvements in both open and binary drivers have forced me to greatly revise my reccomendations. Unless you are absolutely certain that you need a nvidia product, I would reccomend buying a Radeon -- driver support now is excellent for 2d, and 3d is fairly good via binary drivers. Because specs are available, the driver support for these cards will only improve.

The Radeon 47x0 series and the GeForce 2x0 are competitors in the current generation of cards. I would give a fairly unconditional reccomendation to the 47x0 cards. They offer vastly superior price/performance to competing solutions and are effectively the GF8800 of the current generation.

If you would like a discrete card that offers the best power efficiency, the Radeon 3870 is an excellent choice. It's somewhat slower than the 48xx-series, but offers better power efficiency and is still fast enough to run any modern game at high speeds.

My old reccomendations were heavily skewed in favor of nvidia largely because the nvidia binary driver was the only reasonably fast 3d solution in Linux at the time. The situation has now changed. nvidia still probably is currently the highest performance for these generations, but ATI/AMD is not far behind and will only improve, thanks to their generous contribution of open hardware documentation and increased development efforts on their own proprietary driver.

The GF8 is as large of an improvement over the GF7 and GF6 as the GF6 was when compared to the GF5. If you're in the market for a new card, I would suggest buying something from the GF8 series if you can justify the cost.

In the GF7 generation, the 7900GT/7800GT are the clear winners. They offer the best performance/power and price/performance. Faster cards are much more expensive and run at a higher voltage, which means they are far more power inefficient.

In the GF6 generation, the 6800GT is a much, much better performer than the 6800. The 6800 Ultra does not provide a good price/performance compared to the GT. It is also very likely that a GT can reach similar performance to a 6800 Ultra if overclocked. The 6800's 700MHz memory bus and 4 disabled pipelines really harm both its out-of-box performance and its overclockability.

In the GF5 generation, the 5900XT is the only thing worth buying. It, however, suffers from weak shader performance compared to any 6th generation card. This shortcoming will increasingly affect newer games that will take advantage of shaders, but it does not significantly harm older titles.