I recently upgraded the client’s old laptop hard drive laptop to a hybrid drive from Seagate:
Seagate Momentus XT 750 GB
What’s special about it? It’s got 8GB of solid state drive. That makes its speed somewhere between a standard hard drive an SSD. The drive intelligently moves commonly used files to the solid state portion. The hard drive handles all that on its own, appearing to the computer as just one drive.
With the original hard drive in this 5 year old Mac, it booted up in 55 seconds. With the new drive it booted up in 43 seconds. But after three boots, it had moved the boot files to the SSD and was booting up in 24 seconds. It felt much faster for common tasks and commonly used programs.
If you need a large fast drive, this Seagate is a great compromise. SSDs at 750GB are prohibitively expensive. And standard hard drives are much slower.