External USB Drive Caddy & Upgrade Kit - Apricorn
Apricorn has a nice package that includes a case/caddy for a 2.5" notebook drive in both SATA and ATA interfaces are available.
What's really nice is there's an EZ Upgrade kit that includes software, that you boot from a CD and allows you to copy your current drive over to the new one. Then just swap out the drive and you're playing with more space....
Link to Apricorn