I’ve been answering this question a lot on myLot, so I thought I’d post up my responses here for reference.
Simply building a website is not enough, you need to get people visiting it. I wouldn’t suggest using thinks like Google AdWords if you’re new to it, it’s far too easy to lose money on. Start getting links to your sites, one place you can do this for free is by adding a link to it from free web directories. A good list is here: http://info.vilesilencer.com
Try to build reciprocal links with related but non-competing sites; no matter what SEO experts say, you can still get good, relevant traffic to your site from them.
Add a blog, or an RSS feed (say, of your newest products). Everytime you get write a new blog entry, or add a product, ping the site feed using sites like this: http://pingates.com
Add a link to your site everywhere you can without causing problems; eg forum signatures and profiles.