HTTrack is a free software utility that can be used to copy and browse internet sites while offline. It allows users to store a Website, it's images and structure from the internet recursively on a local directory. An HTTrack user can then browse the site and it's links off line as if they were connected to the site via the internet. HTTrack can be run directly from a portable USB device such as a flash pen drive.
HTTrack Portable Offline Browser Screenshots:
Authors Website: httrack.com