Bob Apthorpe has written an open source Posix text filter that calls SpamAssassin:

http://www.cynistar.net/~apthorpe/code/babycart/babycart.html

It is useful as a general spam check on arbitrary text for example from a wiki or blog. It can be used with SURBLs, RBLs or any other SpamAssassin rules.

Jeff C.