PHP frameworks are in great news from 1-2 years in PHP community. Lots of PHP frameworks are available to choose from. Framework is good for development for few reasons. This provides lots of developed code for reuse. All frameworks have community where developers can get help. Discussing your problem there can be easy as all are connected through a common framework. Framework has codes developed by experts so you are also getting help by this. Frameworks use good design principle. It forces many to develop good codes. Though in many cases it can be hindrance for implementing your new ideas.
These days you may get lots of projects, which demands to be developed on top of good Framework. So learning PHP framework can be a good investment for developer.
Frameworks are divided on two broad categories: Full-Stack and Glue framework. Glue frameworks are not tightly coupled and provide greater flexibility than Full-Stack framework. Glue Framework allows advance developer to choose their way to use the existing codes base from framework. Full-Stack framework is tightly coupled so one way it is sometimes difficult to implement your own ideas but other way it requires less work to make things work. Full-Stack framework saves you development time by providing per-built logic for common application patterns.
Symfony - Based on MVC architecture, it is very much in news as a good PHP framework. This comes in Full-Stack framework. Licensed under New BSD license.
CakePHP - This comes in Full-Stack Framework. Licensed under MIT license.
CodeIgniter – Licensed under Proprietary category. This is Glue type framework.
Zend Framework – It is both full-stack and glue type framework. Comes with New BSD License. It is consuming widely available APIs from leading vendors like google, amazon, yahoo!, Fliker and others.
Solar – It is Full-Stack framework, making inroads very fast into great developer minds. License: New BSD.
Prado – Full-Stack type and licensed under New BSD.