pdftk is a piece of GPL software that I’ve been looking for for a long time: It can split, join and otherwise mangle PDF files, which in my specific case helped me submit one of my (many) take-home final exams as a single file instead of three separate ones, reducing the margin for error on the professor’s part. :)
Oh, and of course, Debian’s already been there:
aptitude install pdftk
:)