I use 4 external HDD, 200 Gb each. One for photo, one for family videos, one for MP3 (all legitimate, by the way - no downloads), one for music. Used them for 2 years and I only turn them on when I need to grab something or back something up. No problem so far.
I just buy Western Digital HDD for all of them and I buy a separate external case by Bytecc (about US$30 each, the case, I mean).