A new technology called SSHD is bridging the gap between SSD and Platter based Hard disks basically by providing a solid state (NAND) buffer for frequently accessed files.

The main market appears to be notebook PCs, as they are released in 2.5" format. They can be used with desktop PCs with the right brackets / bays however.

There are several SSHD drives in the market including:

Seagate Momentus XT 500GB Solid State Hybrid Drive (SSH)

Western Digital VelociRaptor 600GB

OCZ Synapse Cache SSD Drive

You can find a range of Solid State Hard Drives below:

Solid State Hard Drives