Codespell is regularly being updated and comes with a dictionary originally derived from Wikipedia. I normally pull the latest updates from the repository before running it against my source code.
Fetching it and using it is relatively simple:
..and it will find common spelling mistakes in the entire project directory. Easy!
git clone git://git.profusion.mobi/users/lucas/codespell cd your-project-dir /path-to-codespell/codespell.py