Automatic backup on a Mac, but NOT with Time Machine?

I would like to know if there is a way to automatically backup my MacBook, without using Time Machine. Time Machine only backs up what is ON your computer, and I want to use my external hard drive to keep some things off that I don't need often, in order to conserve memory. (ie, Save old photos on the external so as not to fill up the internal.) However, I'd like to be able to plug in my external hard drive and have it automatically back up (like syncing an iPod) some things, like music, new photos, etc. Is there a way to set this up, so that it won't sync with the WHOLE computer (thus forcing me to leave all pics on the computer, or force them off the external eventually when it fills up as if using Time Machine), but only sync with certain parts of the computer?