Jonny
Are you looking for portable/travel solutions or home use?
For home use, consider using Addonics Port Multipliers. With these gadgets, you can use an old PC case ( which can be bought at the local Salvation Army or 2nd hand store) and install up to 10 drives. There is a hardware RAID version which is only a tad bit faster for random read/writes (mostly due to the processor overheads)
For drives, I now use the Western Digital RE2-GP drives now. They use about 40% less electricity than normal drives and are only about 10-15MB/s slower. With a 6 drive RAID 0, I can still use them for 4:4:4 HD uncompressed or even 2k work.
I will say that the 1TB drives have been less than reliable thus far. Eric Cheng had 2 of 6 Hitachi 1TB DOA. I just added 2 1TB WD RE2-GP as a test for reliability vs the 750GB I have already.
For portable location solutions, editing in ProRes 422 with FW800 drives, I use the La Cie Little Big Disk (limitations: IDE/PATA connection so 500GB is max support for now). The Gtech Mini uses SATA so they can be upgraded to 640GB (2x320GB 2.5" drives) but it's a lot more expensive.
The last location we were at, the HD engineer had a minitower eSATA connection to the editing laptop to process dailies in AVC for satelite transmission to the production big wigs.