Estrongs is a full featured file manager, with ROOT access options. It's had it for at least 6 months or more. It's free, it has a file editor, text viewer and more. I highly recommend if you your not willing to pay for Root Explorer. You can zip and unzip stuff in it(just like RE), and it has an app manager for quick access to removing files, you can also access network folders and such(not able to do in RE).
I use both, at some point on a 2.1 rom, ES File Manager wasn't getting full root access so I bought Root Explorer, since I paid for it and switched roms, I still use it. but if I didn't have that issue that one time I would have never bought Root Explorer. Both are useful.