Lukas Smith has posted some of his thoughts on who the framework winners are right now and which might pull ahead in the future including Symfony and Zend Framework.
I have not been that active on the conference scene in the past few years, but the ones where I did attend I also tried to take a peek at what others are doing. Also this post is kind of exploratory to see what other people think, hopefully without inviting a flame fest upon myself. So with this disclaimer out of the way, I think the big 3 frameworks for the next few years will be Lithium, Zend Framework 2 and Symfony2.
He looks at each of his "winners" and explains his rationale behind their selection including community support, features offered and the overall structure and feel of the framework. He mentions two other interesting frameworks of note that have come out of other projects - Flow3 and Nooku. Comments on the post suggest even more frameworks to look to in the future including Yii and mentions of Nette and CodeIgniter.