Replacing internal HD - clone old drive?

I'm planning to replace the internal HD on my Mac Mini Intel Core Duo. Since I've already been inside the unit to replace the RAM, I'm not anticipating too much difficulty with the hardware swap, and have the OWC video to guide me.

I'd like to be able to clone the current hard drive onto an external drive, so that I can migrate its contents back onto the new internal drive without re-installing everything. Any advice on how to accomplish this?