What external HD can I use to my Airport Extreme Base Station for use of wireless Time Machine? The title pretty much says it all.  I currently have an Airport Extreme Base Station and I want to be able to use the USB port on it to hook up an external hard drive and use it as a wireless means of backing up my hard drives, and have Time Machine act just like it would with Time Capsule.

Has anyone had success in setting this up? Is there a specific hard drive that has had success? Any spec I need to be looking for in shopping for a hard drive? Any help is appreciated.
Unlike the Time Capsule, the Airport Extreme doesn't support being a backup destination, no matter what drive you use. It is possible to force Time Machine to use unsupported destinations, but this is unsafe - the AEBS lacks features that help protect data, and without them, the slightest network error can make your backups useless.

Some of the technical reasons for this have been explored here: Why won't Time Machine work with a drive connected to an Airport Extreme?

However, you can look for a network-attached drive that supports Time Machine, such as WD's My Book Live. These are drives that attach by ethernet instead of USB, and they implement the file-sharing features that Time Machine requires.