From Nem's Tools:
GCFScape is an explorer like utility that enables users to browse Half-Life packages and extract their contents. GCFScape supports .bsp, .gcf, .ncf, .pak, .vpk, .wad, and .xzp packages and runs independently of Steam.
What's new in this version:
Version 1.8.4 has fixed support for VPK file format.