Laravel for PHP is my current favorite for backend. V5 should be released this week. Robust, expressive, active community. Provides a more accessible interface to a lot of Symfony components under the hood.
Zurb Foundation is my current favorite for frontend. It embraced SASS (which I prefer to LESS); there are SASS ports for Bootstrap but the fact that they haven't ditched LESS yet turns me off. I generally prefer the flatter look of Foundation's components as well.