The one's that have so far worked for me are

www.specialtech.co.uk, It is the USB2 / Firewire 5.25" Lightbar enclosure (Mine is Prolific PL3507 Firewire chipset). It is currently plugged into my firewire port and reports a 42MB/s transfer (again I think this is false but have not tried a 16x burn yet to check), I have not checked USB2 either but will get around to it when I get firewire working correctly

I have also purchased the 2x 5.25" firewire case they have but I am having a few problems with the Firewire interface card & getting it to talk to my unit (keeps acting funny). Its an Oxford card & it keeps loosing the firmware so I keep having to re-flash it when I adjust some settings.

I have also had luck with a USB2 only case from Belkin, however you MUST make sure it has the ALi chipset as the one I purchased didn't and it did not work correctly (quickest way to tell is to burn a DVD+RW at 2.4x and wait for a freeze), however saying this enclosure work correctly is a bit missleading as it failed to burn ANY CDRW or DVD- discs. I dont know if its my discs or the enclosure until I have time to check them in the new one.

Ill keep you posted