blam!

we like to see comments on our blogs. activity on our pages let us know we are doing something useful to others, something that generates interest and thought in at least one or two people. however, i have noticed commercial commentary on a number of blogs, especially those of some of my classmates. i guess this is not a new phenomenon, but blog spam or blam seems a bit less checked that email spam. the conspicuously translated wording is very similar to the various viagra (and herbal analog) spam messages i get via email. does anyone know of a filtering widget or service that can help reduce these abusive commenters without blocking desirable contribution?