Upgrade your large capacity spinning drive with this special 2.5" SSD and Integrated Dataplex™ Caching Software from OCZ
This drive/software combo looks intriguing, at least in theory, especially if it's just one big cached bootable C: drive you wind up with (it appears so).
Looking forward to hearing from others as to how it (well) it actually works, but this appears to be the closet we have to a follow-on to 2010's Seagate Momentus XT Hybrid that maxed out at 500GB.
Sep 27 2011 Update:
Yes, it appears it's just one drive letter, OCZ apparently gets their software from
It also appears Diskeeper is in this same SSD caching software for OEMs space
Oct 09 2011 Update:
Here's another company (in beta) with read/write caching: