For free - Total Commander
I use Advanced Explorer and I am very happy with it. There used to be a freeware version of it but it has been superceded - If you want that PM me and if I can find it I'll email it to you.
Resco has a good reputation and does included a well regarded registry editor - if you need one of these for free PHM have one.
It's horses for courses try a few until you find what you like best.
Google for them or try
www.freewareppc.com