Here's a program that you might want to keep an eye on, as it might well open up another revenue stream for your site, one that's far more low-key than AdSense itself...This is an email message I received from Google about being included in their new beta program. I'll post more as I see how it works!

Dear Publisher,

Congratulations, your account has been selected to participate in the AdSense Referrals Beta. The Referrals Beta is an exciting new feature of AdSense that allows you to:

• Earn extra revenue on a cost-per-action basis
• Select ads from hundreds of AdWords advertisers as well as our standard Google product offerings
• Select a list of relevant keywords for your site and let Google figure out the best ads for your site
• Customize your referral ads to match the look and feel of your site
• Track the success of your referral units with custom channels

letter continues...

When creating a new referrals campaign, remember that you can select up to 10 keywords per ad unit. Selecting keywords allows us to always display the highest performing ads for your site. When you select keywords, there is no need to search for new advertisers or update your code; when new advertisers that match your keywords are added to our inventory, they will automatically be added to your ad rotation. For help creating your new referrals campaign, please visit our Referrals Beta Start-Up Guide.

Also, when you add your new referrals unit to your site, experiment with different page placements. We have found that ad units that are placed above the fold and within the site's main content perform up to 80% higher than ads placed in marginal space below the fold.

You can also find answers to many of your questions about Referrals Beta by visiting our common questions page.

If you are having technical difficulties with your account or would like to report a bug, you can do so by emailing us at adsense-referralsbeta@google.com

Thank you for participating. Over the next few weeks we will be making various upgrades and changes; we encourage you to login in frequently to see what we are up to.

Sincerely,

The Google AdSense Team