"PolyUnpack: Automating the hidden-code extraction of unpack-executing malware"
http://www.acsac.org/2006/papers/122.pdf
OllyDbg' plug-in as well...
http://polyunpack.cc.gt.atl.ga.us/polyunpack.zip
"Classification of Packed Executables for Accurate Computer Virus Detection":
http://roberto.perdisci.googlepages.com/Perdisci_Lanzi_Lee-PRL08-public.pdf
And python script (pefile needed) for entropy calculation:
http://roberto.perdisci.googlepages.com/PEPackerInfo2.0.py