Want to write some miscellanous Common Lisp code?
Rosetta Code is a wiki where a variety of programming problems and language features are demonstrated in many languages, allowing language learning and comparison of features and paradigms.
If you'd like to contribute Common Lisp code to the project, I've just completed a classification of tasks in CL (like my prior one for E), so that it's easy to find the kind of problem one wants to work on at the moment.
One thing I find interesting about working on Rosetta Code is that many tasks bring with them some particular perspective - someone's notion of how programming necessarily works - and it can be a challenge to figure out the analogous way, or best way, to do it in your language is, and then explain it.