I originally come from the PHP world but have been using Django (a python web framework) since a few months. I am really impressed by the quality, the features and the extensibility of this framework !
Concerning PHP, I am a big fan of CakePHP.
A useful start to have an overall view of PHP and non PHP (Ruby, Java, Python) frameworks :
http://www.therightsoft.com/softwaretechnologies/webframeworks