The easy way to do this is by setting up autofs. This will automatically mount configured filesystems whenever you attempt to access the mount point and will unmount it after it has been inactive for a certain amount of time (like 1 second for USB drives). I use it for all of my removable devices and it works quite well.
To use automount, you need to have auto mounting support enabled in the kernel and make sure you have the autofs package for userland utilities. If you have multiple USB storage devices and a 2.6 kernel, it's also a good idea to set up some udev rules to create unique names for each of your devices.
You can google for autofs and automount tutorials on the web. You might also consult tha man pages for autofs, automount, and auto.master.