I use an in-house script to stop form spam on the "Get Included" page of a sphider based web site. Actually I'm using it on all my sites. People have been asking to use it so I went ahead and released it to the public. I know it's not technically a mod for sphider, but I think many will find it quite useful.
It's simpler to implement and far easier to use than others that exist already.
For the features list, instructions, source code, support and to give feedback on what you'd like to see in future versions:
Stop Form Spam
Here's how it looks on the sphider based site:
Florida Search web site submission form.
