With Source Finagler you can open and browse the contents of GCF, VPK files, etc.
It assists in relocating SteamApps folder to a different location by creating the Steam Apps shortcut (symbolic link).
It "Helps" Source-based games so other Mac OS X applications can properly recognize them as Mac OS X applications. (Use this with apps like USB Overdrive, SteerMouse, Logitech Control Center, etc.). It includes Source Texture Image (VTF) and Microsoft DDS (DDS) QuickLook and Spotlight plugins. Double-click VPK files in the Finder to automatically copy the file to the appropriate game's addons folder.