http://en.wikipedia.org/wiki/Comparison_of_web_application_frameworks
Since we are ambitiously aiming to be big, scalability is important, and so are globalization features. Since we are starting out without funding, price/performance and cost of licences/hardware is important. We definitely want to bring AJAX well present in the web interface. But apart from these, there's no further criteria I can come up with.
I'm most experienced with C#/ASP.net, PHP and Java, in that order, but don't turn down other languages (Ruby, Python, Scala, etc.).
How can we determine from the jungle of frameworks the one that suits best our goal?
What other questions should we be asking ourselves?
Reference material: articles, book recommendations, websites, etc.?