Almost all of my external drives are triple interface - so USB2, Firewire 400 and FireWire 800.
I have......
4TB Western Digital My Book Studio Edition II - set up in Raid 0 and used for my iMovie projects/content.
4TB Western Digital My Book Studio Edition II - set up in Raid 0 and used for all video files imported from my camcorder.
2TB Iomega Minimax - sits under my Airport Extreme Base station (fits perfect) and is used for accessing files over the wireless.
2TB Western Digital My Book Studio - used to backup the Minimax drive above.
640GB Western Digital My Passport Studio Edition - used as my Final Cut Express scratch disk.
640GB Western Digital My Passport Studio Edition - used for backing up all my photo collection etc, and also has a partition for my SuperDuper image.
1TB Western Digital Essential - formatted as FAT32 and used to share files between MAC and windows machines.
So a fair number of drives!
All the drives above all have USB and Firewire800 - I prefer firewire800 since I find its much faster the USB2. Saying that all of the drives also have USB connectivity should I need it. The only exception is the 1TB Essential drive, which is USB only.
A couple of videos I made of the drives.....
I have two of these 4TB drives, which are set up in RAID 0 (Mirroring).....
http://www.youtube.com/watch?v=rUbBdAuzxXk
Some of the drives (but not all!!).....
http://www.youtube.com/watch?v=D_OX03uaLk0