LordPE is a tool e.g. for system programmers which is able to edit/view many parts of PE (Portable Executable) files, dump them from memory, optimize them, validate, analyze, edit, ....
Main features:

* Task viewer/dumper
* Huge PE editor (with big ImportTable viewer, ...)
* Break'n'Enter (break at the EntryPoint of dll or exe files)
* PE Rebuilder

I personally use this tool along with XVI32 and olydbg to add code caves into the PE file so I can manually pack and XOR malicious code into the PE file.