I just setup  Recaptcha to help combat comment spam. While Akismet does a good job, recently more and more comments have been getting through its filters. Recaptcha is a project being developed by Luis von Ahn at CMU (previously mentioned on this site). One nice thing about the Recaptcha project is that it makes use of the effort to improve OCR (optical character recognition) accuracy. Captchas are generated from scanned text and the results are used as the digital interpretation.