http://www.decimus.net/synk/

Synk is a great utility if you're using any sort of removable media, like a USB flash drive. It allows you to synchronize files and folders between different volumes of folders.

I carry a flash drive that has all my USF related materials on it. Synk allows me to keep everything properly synchronized between it and multiple Macs.

Best of all, the author will let you use it for free if you're a college student. However, if you can toss him a few bucks, it wouldn't hurt - he's a grad student. . .