There's no difference between SATA 3Gb/s and SATA 6Gb/s on HDDs - there isn't a HDD that can put out data up to 3Gb/s so SATA 3Gb/s is fine and no different.
The Hyper 212+ that gkay09 recommended is a good choice and the price on that Lian Li case is really good. I also agree on the GTX 570.
An SSD is a nice upgrade in a lot of areas like boot times and random reads/writes but it will not improve gaming performance much because games don't spend too much time reading from the disk. You will get better load times between levels and things but it won't increase your fps or anything.