PCMan File manager, another lightweight alternative
There are plenty of file managers available for GNU/Linux and probably most of them are lightweight. However the most popular ones are not among the lightest ones because they are usually a part of a bigger default complete system or contain features deemed necessary for the full desktop experience, or well whatever the justification or reasoning for including them is. The ones I'm talking about are pretty much nautilus and konqueror.
Most of the lightweight managers probably look a bit geeky, at least in acting in a way that most people would not expect them to (be that better or not) so they're usually chosen by people who like trying out new ways of computing, or in this case just managing their files.
So, until now if anyone asked me to recommend a good familiar looking yet lightweight and faster file manager I'd recommend thunar, but now I stumbled (not with a stumble extension mind you ) on another one worth a try: PCMan File Manager through this blog. If you're on GNOME or Xfce it being GTK based will make it fit right in. It also acts alot like nautilus and thunar, but is much faster and has tabbed browsing just like firefox. To open a new tab just click a plus icon.
It also allows opening a directory with super powers (sudoing or as root) from a right click menu and opening a current directory in terminal from the tools menu, which I find quite useful.
Another interesting thing I noticed in its preferences is that it can render the desktop (icons and wallpaper) which is a great thing to have if you're using a window manager that doesn't manage the desktop as well.