Zend Framework is a good foundation for everything and can be used also as just a library of various functions. It is also the closest thing to be an "official" PHP framework so there are a lot of developers who know how to use it. It is, however, not a framework you would use to prototype something very quickly.
There are several frameworks that could be used as a quick RAD (Rapid Application Development) tools.
A good example is CakePHP, which is a very popular framework. Fairly easy to learn. It has a lot of sensible defaults and naming conventions that make your life much easier, but which you can override. Continue reading PHP MVC Frameworks