A few months back, I had a contact form (on a Drupal site) with a spam problem. It wasn't something I was interested in spending a ton of time on it, so I set up ReCAPTCHA. Problem solved, but I didn't feel great about the privacy implications. So, my question: What should I have done? Specifically, I'm looking for an alternative to ReCAPTCHA that is:

* simple to set up—not much more complicated than ReCAPTCHA

* free or quite cheap

* reasonably effective, at least against generic spiders

I'm not sure if such a thing exists, but I think it needs to if we are to have any chance of moving people off ReCAPTCHA.