MistyPE is an excellent WinPE generator based on Winbuilder.
It is minimalist (in a way it is easy and fast to build WinPE) but still very flexible so that one can add many extra softwares in there.
Download/Discuss it here.
How to use it? Easy :
-Go to source tab,
-Select your source directory to point to your windows media installation dvd drive (E:\ for me),
-Retrieve your winpe iso in x:\MistyPE\MistyPE.Project.Output\.