SATA III (6 Gb/s) refers to the data transmission rate between a motherboard and a device such as an ssd, hard drive, or optical drive. In theory the data transmission rate could be as high as 6 Gb/s. However, for a variety of technical reasons the actual rate is much lower.
SandForce refers to a company that makes controllers which are a component of ssd's. The SandForce controllers are very popular.
Within the next few months you will be able to purchase SATA III capable ssd's that are also equipped with brand new and improved SandForce controllers. One example would the new OCZ Vertex 3 Pro which will be SATA III capable and equipped with a brand new SandForce 2000 series controller.
Here is a link to an article about the new drive published by AnandTech:
Scoopsy, There is no such thing as SATA 6, I believe you are referring to SATA III (also called SATA 6Gb/s). If you must buy now, go with the RealSSD as it already uses SATA III. If you can wait a bit, check out the newer Sandforce drives when they are released, you might like their performance better than the RealSSD drives.