There are plenty of tools out there for creating disk images of your hard drive but there are a few that work specifically with USB drives.
USB Image Tool is a smart little application that's capable of generating images of your USB devices so you can always restore the disk image anytime you need. With USB drives now capable of holding up to 1 Terabyte of data, it's very wise to create images in case of hard disk failure.
The program automatically detects USB devices connected to your computer and scans them before asking you whether you'd like to create an image backup or restore a previously backed-up image. USB Image Tool can create images of USB memory sticks and MP3 players, that are mounted as USB drives. Note that the tool requires the .NET Framework 2.0 installed in either XP or Vista and the usbit32.dll included in the archive must be placed in the same directory as the EXE file.
If you've got a lot of data stored on USB drives, USB Image Tool is an easy to use and space efficient way to protect your information.