Ruby + Ruby On Rails ( Twitter, Group On, BaseCamp, Scribd, Hulu, Justin.TV, SlideShare etc..) The Web Framework is designed for Fast coding for Web, really nice design and easy to use.
Python + Django ( Washington Post, http://www.djangosites.org/most-comments/ ) Django is also a Web FW designed to help in fast coding, but as far as I can see it strong point is the admin console which is very rich.
Scala + Lift ( http://lift.poweredsites.org/ ) I am not very familiar with it, I only know that it's a son of Java language, it uses the Java JVM to work, and it's sintaxe looks more like java then the to above.
I myself am learning Ruby because I liked the Web Framework more( I am a Java programmer, java sucks a bit for Web, too complex I think) Python has the appeal to be useful for more stuff like doing linux stuff or getting a job on Google :D
Cheers from Brazil !