Midnight Copmmander in a shell is fun but not really a GUI.
XFCE uses a nice one called XFE. XFE is my favorite light-weight file browser.
Mozilla or Firefox make nice file browsers.
Not tried this one but it looks cool: http://tactileint.com/interrogator/
ROXFiler is part of a desktop enhabncement for Fluxbox, blackbox, IceWM, etc. It is very nice but kind of non-intuitive. Once you figure it out is is very nice and graphical.
There are about a dozen more here:
If you can't find what you need, come back and we can find some more. Linux is all about choice.