Wordpress anti-spam

Currently I'm using block spam by math (forcing commenters to solve a simple addition) and Akismet to stop Wordpress spam. This works reasonably well, now I get about a dozen comments in my spam folder a day (much less than it used to be). Does anyone have any other anti-spam systems that they can recommend? One thing I'd like is a plugin which only permits one pending or spam folder comment per IP address. -- My Main Blog http://etbe.coker.com.au/ My Documents Blog http://doc.coker.com.au/