Developer PsDev released a new version of his tool for PS3 Developers: PS3 Tools.
This windows GUI allows you to manipulate various PS3 files by decrypting/encrypting them. This latest version allows you to decrypt and extract Retail PKG files.
Credits for this tool, besides PsDev, go to naehwert, KaKaRoToKS, geohot, Math, eussNL and Fail0verFlow.
download PS3Tools here