So I want to buy a new external hard drive that's portable and fast. The Firewire800 drives that don't require power only go up to about 640GB, and ideally I want a 1TB...
Going back to your original posting -- there are FW800 2.5" drive housings available that take 12.5mm high drives. No wall wart needed. Then, get a 1 tb 2.5" drive (true, there aren't many out there, but there are some), and you're good. Installating the drive is easy.
http://oyendigital.com/hard-drives/store/CB2-M.html
There may be other enclosures, but this is the only one I know about.
Then wait for USB3.