Facebook may eventually take American Express, but for now Visa will do just fine. The credit company is plunking down $2 million for an ad campaign on the social network.

As part of the campaign, Visa will give $100 in advertising credit to each of the first 20,000 U.S. businesses that download the brand's web application.

Facebook estimates that there are about 80,000 small business profiles on its site.

While Visa may be just one account, the name goes a long way to helping Facebook, which has had trouble convincing advertisers that social networks are a good way to reach users.

But for Facebook to really make its case, Visa's widget will need to cut through the clutter. According to an Associated Press report, there are more than 24,000 widgets on Facebook. However, the $100 incentive should go a long way to raising Visa's profile on the site.