Amazon S3 Monitoring Service from Monitis
From the Monitis recent Press Release: "Monitis Inc., a leading provider of hosted enterprise-class systems management software, launched a new cloud monitoring service. Monitis provides user-friendly, cost-effective systems monitoring through a software-as-service approach. Monitis’ on-demand cloud monitoring service is now enhanced through Amazon S3 monitoring. This new ability, Monitis S3 Monitoring, lets customers independently monitor their S3 usage and storage, and notifies customers when they reach prescribed thresholds. Monitis thus provides its customers with greater access and control over the cloud infrastructure." Read more at http://blog.monitis.com/index.php/2009/09/01/monitis-launches-on-demand-cloud-storage-monitoring-service/ . Monitis already supports Amazon EC2 Monitoring