Good Form Security - no CAPTCHA

Question

Is there a good method of form security that does not involve CAPTCHA? CAPTCHA is so annoying, but I need security because I am getting form spam. My form is

Answer 1

Math questions are interesting alternative. You can even write your own simple math checker by using random numbers.

Here are couple of plugins:

http://www.codegravity.com/projects/mathguard

http://sw-guide.de/wordpress/plugins/math-comment-spam-protection/