![snippet snippet](http://www.alonsoruibal.com/wp-content/uploads/2009/06/snippet.png)
With pdftk we can (as well as a lot of other PDF-related operations) join PDFs in Linux, wich is something very useful. This is one example:
# pdftk file1.pdf file2.pdf file3.pdf cat output file_output.pdf
For windows there is also Pdftk Builder, with a graphical interface.