Now, if this is already available through a hack or plugin then please don't kill me! :)

Anyhoo, something that I would like to see is visiting commenters having to input a randomly generated sequence of numbers from an image. You know, like most registration forms have.

I don't know what it's called, but I think it would severely decrease comment-spam. At least for me, I get maybe 50-100 bullshit comments a day that somehow get through the antispam filter (and yes, I do keep it updated).