Synching HDD to External HDD - What To Use?

I used to have a great program on Windows to synchronize files in my Docs. It would sense the changed files and copy them over to my HDD (or oder files, or whatever I specified). I now there's probably something like that on OSX already, but I'm still finding stuff out. What do you use for synching & backing up info that way?

now you have something even cooler built right into your OS

Time Machine

Awesome. I'll look at it. Downloaded Backup 2.2.1 but looks like I don't need it!

P.S.: Love your avatar!

Time Machine worked beautifully for backing up and I will continue to use it. However, I have files on old PC and laptop which I'd like to be able to copy ONLY newer changed files, so I don't overwrite web pages I've made with old versions, for example.

What would be good for that?????? With 3 or 4 different sources, it's toooo confusing and tooooo many files to do manually.