Tired of ASP.NET, which of the following should I learn and why?
Learn Ruby on Rails. It'll change the way you see web development. It did for me!
A valid alternative is Django and Python. I don't use it, but I consider it to be just as good as Rails.
Which of the following technology is easy to learn and fun for developing a website? If you could only pick one which would it be and why

Clojure/Compojure+Ring/Moustache+Ring
Groovy/Grails 
Python/Django 
Ruby/Rails
Turbogear
Cappuccino or Sproutcore
Javascript/jQuery