While OCZ just released the Revodrive Hybrid, they now also launch a seriously fast SSD just for caching. Combined with their Dataplex cache application software and your own HDD, the combination could be just what you are looking for, all at a much better price as well with no limitations to your hardware setup.

It's armed with a SandForce 2281 controller and the means to use it, as alongside the SSD you get to use the very same cache software layer the RevoDrive Hybrid uses, Dataplex. A cache in combination with the Synapse SSD offers read speeds of up-to 550MB/s and write performance of up-to 490 MB/sec.