The Gutenberg Galaxy is available online through Questia.com, but you have to pay a fee to access it. I've prepared a Guide to the Gutenberg Galaxy that might help you work your way through the book.

Some excerpts from Understanding Media (1964), the book published after GG, can be found on the TAO (Theory into Action) website.

The McLuhan Program in Culture and Technology is the official home of McLuhan studies. The Program is physically located on the campus of the University of Toronto, where McLuhan spent most of his career, and it continues to offer course work in the McLuhan tradition. Check out the Program's weblog--all the techno-savvy academics are blogging!

Wired Magazine, one of the most influential magazines about techno-culture, has featured McLuhan a few times. In January of 1996, he was on the cover of the magazine and he was the feature story. More recently, one of their reporters reviewed a new documentary, McLuhan's Wake. Both pieces play up the clownish side of McLuhan's career, but I am still convinced that he was deadly serious about joking.

I have made a handful of entries about McLuhan on my weblog:

A summary of a criticism of McLuhan's determinism.
Learning to unlearn--McLuhan would like this idea.
Another critic of McLuhan seems to get him wrong. The full essay here does have some useful lists of print culture features compared to electric culture features.
Understanding the Web is an application of McLuhan to the medium you are currently using.
One of my first entries--expressing my argreement with McLuhan that education needs to be playful.

This old page on "Electronic Communication" uses Ong's eras (orality, literacy, secondary orality) instead of McLuhan's terminology, but Ong and McLuhan more or less agree. This page focuses on the electric era.