a@b.com!
Yeah if your email address is on websites somewhere then you are hooped. Bots troll the web automatically looking for email addresses to add to their database.
The only way then to reduce the spam is to use spam filters. I also use gmail, partly for this reason. There are 3rd party spam filter programs out there as well that you can install, though I wouldn't know which ones are effective.
And really there's no reason for your email address to be on a website in clear text where it can be harvested. There are many different ways to have the same functionality (allow browsers to the site to contact you via email) without exposing your email address. Only problem with that is once the cat is out of the bag... unless you change your email address, which for a business can be impossible.
Plus if your name is fairly common, spammers will send to it as a matter of due course.
bob.smith@telus.net (and
bob.smith@gmail.com,
bob.smith@whatever.com) is a good bet to spam to. I get the odd spam on a few private accounts because of this.