I have just installed an OWC Data Doubler kit in my 13″ MacBook Pro (the late 2011 model). It is a bracket that replaces the optical drive that ships with the MacBook Pro and allows you to install a second 2.5″ hard disk or SSD. In my case I have installed a 480GB SSD (KINGSTON SV300S37A480G Media) in the location of the original disk and moved the original disk to the Data Doubler. The boot disk is now the SSD; I intend to use the old disk as an internal backup drive.
The instructions are very good, all of the tools required are included and the kit itself is of a very high quality. I highly recommend the Data Doubler kit (and the idea of installing an SSD into a 4 year old MacBook Pro to give it a new lease on life).