Alternate ads - allows you to utilize your ad space in the event that Google is unable to serve targeted ads to your page.
Alternate Url - provides a 50/50 Revenue Share, full global coverage monthly payments automatic referral income, family safe ads, paypal supported and gives detailed stats.
AlterNut Ad - pays you a flat rate every month in return for you displaying thier ad rather than the PSA. Invite only.
Default Ads - load your affiliate or other ads into DefaultAds and generate a link to include in your Google Adsense alternate ad URL. They show their own ads 1 out of every 100 impressions for this service.
Adsense Chats and Forums


Inside AdSense blog - Official blog that posts new tips and information about new AdSense features.
Adsense Help - Google group for adsense support. Only posts from user ‘AdSensePro’ are approved by Google.
Digitalpoint Adsense Forum - discusses Adsense payments, guidelines, stats and reporting and much more.
Webmaster World Adsense Forum - Discussions around Googles Text Ad service AdSense.