Just installed Growmap Anti Spambot Plugin (G.A.S.P).
This blog has been plagued by spambot comments, and I wanted to try something other than Akismet. G.A.S.P. works by adding to the comment form a simple checkbox which must be checked before the comment is accepted. The default prompt for the checkbox is
Confirm you are NOT a spammer.
UPDATE @ 3/21/2016: As you can see in the comments, I stopped using G.A.S.P. and started using Shield, formerly WordPress Simple Firewall, in October, 2013. It’s my standard, go-to plugin for blog sites. As of this writing, it has a 4.9 rating (out of 5) based on 356 reviews.