...or Google Appengine
Google's Appengine is a different type of cloud - a lot higher level, so you don't have to worry about the OS - which is good if you believe Google's sysadmins are better than you, and bad if you want to do low-level tinkering (using any port but http, for instance).
Standardising this would be a very different exercise, requiring standardised APIs rather than standardised machine image management.
We need a finer definition of cloud services - maybe "Cumulus cloud" for low level Amazon-style clouds, and "Cirrus clouds" for high level Appengine-style offerings.