Reducing Spam help

[fowler1416]

I was told that the Question and Answer was probably the best way to reduce spam. It seemed to work well for a while but now we are getting over run with spam accounts registering. They seem to only hit the blog, which isn't used often, but it is really inflating the numbers which I would like to keep realistic. I have 2 Q&A's setup. Is there a plugin or a better way to stop these annoying registrations?