Your SSD won't b e limited by SATA-2 performance, unless you work with very large files, like 1080p HD movies.
Small file performance isn't even remotely close to SATA-2 max performance, and this what 99% of your files you have (if not 100%), on your system, including games. So you will not see any benefits with a SATA-3 card, unless, as mentioned, you work with very large files. BTW, if you are thinking: "Well I have Blu-ray backups or 1080p movies on my system, and I play them", video players stream the content from your SSD, so you will not see any performance increase there as well.
So get your favorite SATA-3 SSD (I recommend synchronous ones as not only they are faster, their benchmarks reflects more real world results, but also they support significantly high amount of writes over asynchronous memory based SSDs (that is they warranty is 5 years, and not 1 to 3 years)
So that means SSDs like:
-> OCZ Vertex 4
-> Corsair Force GT series
-> Corsair Neutron GT series
-> Samsung 830 series
-> Intel 520 series
to name a few.
