I recommend Thermaltake BlacX Duet with internal hard disks. The brand of hard disk is less important, though I would personally go with Western Digital, Hitachi or Seagate. You also should store the hard disks in ESD bags (I buy them at staticbags.com) and away from obvious hazards when not in use. I've had lots of bad luck with external hard disks, so I don't buy them anymore. They are just the same thing underneath, but usually hard disk companies use the least reliable hard disk model they have to save on costs (unless it is really expensive). The other benefit of having the internal hard disks is that you can configure them to boot any computer you have (and not just use them externally) inside the computer itself. Also, if you have OS X 10.6.5, you can now format your disks exFAT in Disk Utility and use the disk seamlessly with either Windows XP or later with exFAT support installed for XP or OS X 10.6.5 or later, though you'll want to select Master Boot Record partitioning if you plan regular use with Windows. The only thing I haven't tested this with yet is my AirPort Extreme, but it isn't really necessary in that case since it can read/write HFS+ partitions straight from the router.