You'll find similar services (though less of a selection) at Half.com (part of eBay), and of course you can always try your hand at dealing on eBay itself, which is still a popular venue for selling new and used merchandise, though one drowning in noise.
Think SEO, All the Time
Don't underestimate the value of optimizing your Web site for Google. But you don't need to pay an expert thousands of dollars to optimize your site for you: Check out the expert advice from SEOmoz and other search engine optimization writers to learn the basics of SEO, and instill your site with good SEO habits from day one. It takes time for the engines to get to know your site, so be patient. (Just make sure you've submitted your URL to all of them!)
Get Bonus Income With Google AdSense
Unless you're selling physical merchandise, try adding Google AdSense ads to your site. You might pull in only a few dollars a month while your site is small, but that's more than nothing--plus, it opens the door for bigger ad opportunities down the road.
Constantly Promote Your Business
How do one-person businesses get big? They're always promoting themselves--always. Add your URL to your e-mail signature. Create a Facebook group for your business. Write a humorous blog about your product or industry (check out Chris Lindland's Cordarounds blog for ideas). Submit your gems to Digg, Reddit, and StumbleUpon. Comment on online stories in your field and cast yourself as an expert. Meet and greet at trade shows. Make T-shirts, stickers, and business cards. Give away products to charity events in exchange for an ad. Hold contests for freebies and make people work for the prizes. Above all: Don't let anyone forget about your new enterprise.