There are a number of books on Project Gutenberg (and elsewhere) that would make good additions for the CCEL. They have to be converted to ThML (the CCEL's XML-based markup language) in order to be added. In fact, there are some books already at the CCEL that still haven't been converted to ThML.
This process requires some knowledge of XML, but it isn't too difficult for someone who knows something about XML and can use a text editor and XML parser (or XML editor). It would be helpful if they can also run a couple of perl scripts that are already written.
This work is the main bottleneck in adding books to the CCEL.