Search engines like to index sites that are listed on other sites. One thing you should do if you haven't already is to start posting in the MM forum. The search engines are in the constantly and they will index your site from the signature in your posts. The more times you post, the more likely they are to want to go see your site. You should also be active on other forums related to your business. Make sure that you have your link in your signature.
Use meaningful text in all of the Meta description tags for your site .
If you're using a 'splash page', you might consider losing it. It doesn't really benefit your site, your rankings, or anything. The faster the customer can get to the goods the better :)
You should use the Froogle feed. Check the forums on tips to do that.
If you sell on ebay, use your ME page to link to your site. Anytime you ship something put a flyer in the box with your website on it. Give people a coupon to use on their next purchase.
Visit http://selfpromotion.com and read every page! He has some great tips there. Throw him a donation as he works really hard on his site. You can learn a lot there.
Don't rely on search engines. Word of mouth is your best bet. Best of all it is free!
Most importantly, don't give up too early. All of this takes time.