hey Zarak,
I have two 500GB Western Digital "MyBook" Premium Edition drives connected via FireWire on my Mac and I love em! fast, good looking and great bang for the buck. Costco has been carrying them of late at really good prices. it doesn't have a fan, and it sleeps automatically when it's not been accessed in a while so the volume is pretty low. however i've found it to be slightly louder than the Seagate OneTouch units (I have one at work and love it) but the OneTouch case is a little bigger and less attractive (if that matters).
If you are going to use this with an HTPC I'd suggest building a machine with eSATA capability and purchasing a an enclosure that supports it. your data throughput will be much much higher than either FireWire or USB2.0 -- useful for video and pretty much required if you go HD.
i'd also suggest you get a unit from a drive manufacturer like Seagate or WD as oppposed to getting a drive and throwing it in a cheap 3rd party enclosure. peace of mind if you run into warranty issues...
hope this helps. good luck!
-s
