What can I do to stop spam

Unplug your internet connection. If you have no email address, you have no spam. Other than that, welcome to the wonderful world of free speach and "On-line Entrepreneurs". At least that's what they THINK they are.
I run a $2000.00 software package that performs heuristic, wighted examinations of ALL email in and out of the network. I still get some spam although it has dropeed by 75%.

One option is that you can change your address. It's the most drastic, but gives you the opportunity to start over again.

What IS your address? Is it possible that you were hit with a dictionary attack and the html saw that you read it? [pat@company.com is an easy target.]

If it wasn't by the dictionary attack, you or someone else gave out that email address. You have to figure out where, so you don't do it again.

What email server are you using? If it's in your control, you have many options. SpamAssassin for Linux is pretty popular, there are many option for Exchange, etc...

You can outsource the filtering of your email, too. You simply point your MX to the filtering company, and they send you what they think you shouldget. I think Ford Motors does that, if I recall.

I just bought Corvigo MailGate, which lessens the burden, but it's certainly not focused for very small shops.

There are all sorts of filter software programs you can buy. I have heard good things about Spam Cop but do not have personal experience.

Also one thing you can do is to not use the preview mode, or view spam in any way. When previewed or viewed most spam has html code that will tell a server that the e-mail has just been looked at validating your address. Just delete the mail without looking at it in any way.

Good luck,
Dan