Monitoring Cloud health
Both Amazon and Google (and probably others as well) provide web pages which monitors its service status. The one which I go to, when I need to compare availability and to detect service problems is the one called Cloudstatus by Hyperic.
They try to monitor most of the individual services provided by Google (Engine, Datastore, Memcache, Fetch) and Amazon (EC2, S3, SQS, SDB, FPS).
On top of online graphs, you can also subscribe to twitter status updates which can be really helpful during a real outage.