We are trying to decide what the best web framework available for
rapid prototyping in developing our new web application, so we are
hoping to gather information about the frameworks that are out there.

It needs:
-to have many available and compatible development tools (and support services)
-to have many open source user contributions
-to be free or reasonable in price
-to have user management tools
-to support Java

We would like the answer to layout the advantages and disadvantages of
these characteristics of several different frameworks.  Some of the
frameworks we are considering are .NET, Ajax, and Spring.  We would
like to know about these and others you may suggest.

Other information we would like about these frameworks:
-examples of sites which use these frameworks

The answer should be geared toward computer programmers.