The bumping list was a list that used to be bumped in the forum before the section on the main page took over.
It contained links to a countdown website, the latest frame, Primis' .gif, Aubron's website, Explain xkcd's article on Time, lists of end of comic theories, off-topic discussions, and possible meanings, and the answers to two common questions (what are newpix?, and about the javascript).

An example can be found here.