Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
Cloudlytics - Analyze Your Amazon S3 & CloudFront Logs.
AppDynamics - Get real-time insight from your apps using Application Performance Management—how they’re being used, how they’re performing, where they need help.
Qloudstat - Analytics & monitoring for access logs in Amazon S3, Amazon CloudFront, Google Cloud Storage and Rackspace CloudFiles (Akamai CDN)
Zabbix - Track, record, alert and visualize performance and availability of IT resources
Checkmk - Checkmk - the software for effective IT monitoring