A good and commonly-used one is Acronis True Image, and it does a LOT more than just cloning. Better news yet, maybe: you can get it free. Both WD (Acronis True Image WD Edition) and Seagate (Disk Wizard) have customized versions of this package you can download for free from their websites. BUT in each case they will operate ONLY if the DESTINATION disk (the one you're working on and writing to) is from them.
Make sure you get and read the manual for the software. It can do a lot, and knowing what it does and how can help you. Even in the cloning process there are certain configuration and size settings you probably want to adjust manually because the defaults are wrong.
I've used Acronis - it worked fine with XP, was slightly unstable with vista then with the new computer, win 7 64 bit it is predictably unstable - i gave up on it totally - every time i'd try it'd take 3-4 attempts (each attempt would restart the computer back into windows, or sometimes stop at the DOS screen, linger and then show me inside of 30 seconds, complete backup done when it couldn't have
Acronis support is hit / miss
i'm going to try that EaseUS Todo - Cnet seems to give it good review