Marketing an online business is just like any other business. I like fishing where the fish are. Market in places with high concentrations of people. We have just launched our own online poker store to sell chipsets, poker tables and poker books. In order to promote the website we have entered 5 people into the corporate games poker tournament.
We wore the t-shirts and got a rousing response. You can see the full post here on my poker blog.
The point is the online store built its brand with its target market and I found myself quoting prices of tables and chipsets on the spot. It doesnt matter that its an online business, you still have to market it.