What spam prevention tool/service do you primarily rely on?

[eluser]Derek Jones[/eluser]
The field of spam prevention evolves fairly rapidly, as do people’s preferences for how to combat it, so the purpose of this informal poll is to get a finger on the pulse of what you are employing, if anything, on your CI powered sites. If you employ tools or services not listed here, please reply with them, and where appropriate, I’ll edit the poll to include them.

[eluser]drewbee[/eluser]
I am highly impressed with Askimet, and will be employing it on a forum system I am designing. Any user in the new_user usergroup's posts will automatically be sent to Askimet for processing.

[eluser]Mat-Moo[/eluser]
I didn't know there was a CI Captcha?! But I have used re-Capthca on other sites (not CI ones)

[eluser]davidbehler[/eluser]
I use reCaptcha on my CI sites.

[eluser]brianw1975[/eluser]
I've been using reCaptcha for 6+ months now.

Fantastic free service.