Xfe - Fast & Lightweight File Manager for the X Window System
Xfe (X File Explorer) is a wonderful, fast and lightweight file manager for Linux built using the FOX toolkit with a customisable interface which can resemble the twin-panel style of Midnight Commander if needed.
Xfe 0.19.2 running in Debian Lenny
Why is Xfe different? First of all, it's very lightweight due to the library it uses for its interface. It's true that it may not integrate very well in neither KDE or GNOME, but it supports colour schemes which can change its appearance. Some of the themes included are KDE3, Xfce4, GNOME2 or iMac. Aside from themes, Xfe also allows you to change its default font (Helvetica) so it will match the fonts used by your desktop environment.