Google App Engine enables you to build and host web apps on the same systems that power Google applications. App Engine offers fast development and deployment; simple administration, with no need to worry about hardware, patches or backups; and effortless scalability.
Currently Google App Engine supports Python and Java, still can code in other languages like PHP, Ruby etc using Java runtime to convert final code in to Java.,
The best thing about Google App Engine is it can server up to 5 million page views a month and that too FREE.
Check out it now http://code.google.com/appengine/
PS: We have started to like Python after coding Namaaz Tracker using Google App Engine.