I prefer the lacie mini
it matches the mini, but also provides a little vent room underneath the mac mini which the other similiar drives don't do.
I agree, you don't need a super dooper machine to do that kind of thing the regular mini will do it fine.
You can drop the top of the range intel core 2 duo in them and they are supported by os x as others in the range have them. Lots have done this already.