If you want a lower end card for gaming, then get a Radeon 7750 GDDR5 1GB. Don't pay more for a 2GB version (it will be slightly slower, not any faster whatsoever for gaming) and avoid DDR3 versions like they're a plague.
However, like swilczak said, unless you can't afford better and/or have another reason for being incapable if or refusing to get something better, I recommend a faster card. A Radeon 7850 is an excellent option, but the much cheaper Radeon 7770 is also a good option despite being almost as cheap as the Radeon 7750. The 7750's only advantage is lower power consumption allowing it to be used in systems that have no PCIe power connectors.