I use AntiSpam ACP by Lithium Studios

http://www.lithiumstudios.org/phpBB3/viewtopic.php?f=25&t=4

its EXCELLENT!

Installation is challenging, but if you have installed EasyMod it's less than 1 minute:

## Installation Level: Intermediate
## Installation Time: ~33 min (less than 1 min with EasyMOD)