I've got a Buffalo, cos it wasn't too expensive and could be mounted vertically. I also got it because it came with some nifty backup software to schedule backups and a utility to spool down the drive when it wasn't being used.
Unfortunately the backup software is crap so I use ntbackup and scheduled tasks.
Double unfortunately the spooldown software flat out doesnt' work
I know cos I asked them and they said so
...oh and no fan, so it's nice and quiet.