The best way to keep a spammer from getting your email address is to not put your email address on your website. So best case scenario --- use a contact form. And use one that doesn't require you to put your email address in a hidden input field. And even more important, make sure it has protection from email header injection.
If you absolutely must use mailto: addresses, here's a little trick; write it out to the page using Javascript. I wrote a Perl script a few years back which will do just that. Type in your email address and it will spit out a few lines of document.write which will obfuscate your address. You can then place this into an external .js file and reference it anywhere on the page that you want your mailto: to appear. It isn't fancy, but it does the trick.
