[Blind-sysadmins] USB External Server Backup Drives

Does anyone know of, and perhaps even use, a make and model of UEB external drive which will allow backup of SBS 2011/Server 2008 R2. Ideally I need 2. There appears to be a very limited range of such drives, and certainly the likes of the Seagate Backup Plus (2 TB) do not work. It needs to be something I can remove one from the premises, without getting a hernia in the process. George.