This just came out:
http://labs.autodesk.com/utilities/millerLooks pretty useful.
It can do mesh wrapping (internal feature removal), decimation, smoothing, cleanup (w/ mesh merging) and G-code visualization.
It does tend to choke on bigger g-code files, though. Either crashes, or becomes unresponsive.
Also, not sure if anyone's mentioned it before, but
Meshmixer now has a rather complex support material generation feature, albeit more suited for resin (STL/DLP) printers.