I have an external hard drive that I keep all of my work files on and transfer them back and forth between my Windows 7 box at work, and my Mac at home (I work from home frequently).

Can someone recommend a really good backup utility that I can use on that external drive, to back the files up to my work computer locally, or the other external drive on my machine at work?

I'm looking for preferably a free or open source software, and I'd prefer it to be cross system compatible, although I would also consider using a software that will only work on the Windows box.

Also, I will consider a software that has a price assuming it is a really good piece of software and the price is reasonable (like under $50 or so).

I checked out CrashPlan a bit, but not sure if that's gonna be really what I'm looking for. To reiterate I'm not looking for online backup solutions, just a piece of software that can back up my data to another drive locally. CrashPlan Free seems to offer this, but not sure how good it is (considering their goal is to get me to buy a pay for version).

*NOTE: I'm running Windows 7 in 64bit so I need a piece of software that will be compatible with 64bit OS. My previous software, PC Backup, is not. That's partly why I'm in this boat.