For python, if the work is simple, we use web2py and if we need something scalable or complex we build the stack ourselves based on the combo of dejavu and cherrypy. Lots of components are available in python for different segments of a web application.

For web server/dispatcher/controller I think cherrypy beats them all. Cherrypy alone can take you a long way. For ORM there is sqlachemy, dejavu and storm. For forms there is formencode, for json you have simplejson... let me know if you need something else...