Well, we all complained about how hard it was to find Life Magazine on Google Books. The cries have been heard and Google has created a browse site that allows you to look at all the magazine titles and runs in Google Books.
You can also get a full list by going to Advanced Search, clicking the Magazines radio button (don't put anything in any search box, and leave All Books checked); then hit Google Search. Again, you can switch between List View and Cover View (links in the top right of results page).

The story and the links are on the Google Books blog.