I've been using this for a while. It generates a little encrypted javascript thingy that you put in your html instead of a mailto tag. The result on the webpage looks like a mailto, but the source as seen by the spambots, is unintelligible.

If the person reading your webpage has java disabled, they see a blank space where your address should be. But less than 1% of my visitors have java turned off, so this isn't a problem.

I use it, I like it, and I recommend it. It's simple, easy to use, it works really well, and it's free!