I have a 2tb wd black sitting here but I need an external housing so i can connect it to my iMac .. was looking for something reasonably priced and not too big .. i want to mount it on a little shelf on the back of my iMac .. thanks
There are USB 2.0 enclosures and docks for as low as 10 and up to 50 .
Firewire 800 enclosures cost a bit more due to the chipset, and they can cost 40 to 80 .
Maybe have a look at Amazon, or if you are US bound, OWC or Newegg.
MacAlly is a recommended maker of external enclosures, but know, that that enclosure only has Firewire 400, which is a bit faster than USB 2.0, but not as fast as FW 800. If you only want it for backup purposes or data access, it is more than okay, but if you move lots of data (several dozen GBs) on a daily basis, FW 800 might be more to your liking.
The difference (haven't seen your edit yet) is, that the second HDD has Firewire 800.