Leafpad - http://tarot.freeshell.org/leafpad/
A gtk+ based file editor. Lightweight and fast. Requires gtk+ > 2.0.
Tea - http://tea.linux.kiev.ua/
Another based on gtk+, requires 2.4 or newer. A lot more features than leafpad, but no gnome dependency.
These are two editors I have tried. Both pretty new in development, but do what they claim to do. You can always search through the 250+ editors at freshmeat if they don't meet your needs.
As far as filemanagers I am hooked on Konqueror and the shell, so I haven't tried any others. I have no need to keep things slimmed down here.