It really depends on what you mean by popularize. Then it also depends on how you make money form the business. Do you make money only from advertising placed on the site? Do you make money form the selling of physical products that need shipped? Do you make money for selling information products or do you jsut resale other businesses products and they drop ship for you? Do you make money consulting or service based business?
How much is each customer worth? For example do you know what the average customer spend with you over a year? You would not want to spend money on advertising that cost more or even close to your average costumer value. If your average customer value is $5 then you have mostly free options available to you, but if the average customer value is $1000 then you could do PPC or email campaigns, do magazine ads, radio spots, just about anything is open at this level.
Article marketing is one of the best free ways to promote your site.
However, I fond one of the greatest marketing ideas and it is in a FREE E-book
http://www.supertips.com/ultimate/x/?id=3655
I wish you the best of luck. You can Pm me if you want to discuss this in more detail I would be glad to try and assist you with this.