I usually go with Nvidia when I buy graphics cards, but AMD's new flagship card, the Radeon R9 290X really has my attention. It's definitely a high-end card that can compete with Nvidia's Titan, but it comes at a much more affordable price.
AnandTech and Tom's Hardware both have reviews up already, and the benchmarking results are incredible. On most of the games they tested the R9 290X on, it always came in either right below or above the Titan in how many frames-per-second it could handle. The Titan will still set you back around $999, so this new card from AMD looks to be the best bang for your buck right now.