If you're unhappy with your IDE (for whatever reason), you might want to try out Netbeans. The PHP support is rather new and not too stable yet, but apart from the download package being really small (the zip file containing both windows and linux binaries is only 30mb large - 90mb unpacked), it provides some really nice features/advantages:
- No more "Building workspace", indexing of projects takes seconds
- It's really fast
- Very easy, good and fast renaming functionality (in the source code). Just type Ctrl+R, when you're on a variable or method and all the occurences in the file are renamed at the same time
- It's open source
Apart from that, it provides standard features like CVS / SVN support, defining projects and so on.
I have used Zend Studio for Eclipse so far (which is already quite good in my opinion), but I was really impressed how good Netbeans is when Petr Pisl demonstrated it to me at the International PHP Conference 2008. Since then, I'm only using Netbeans. According to Petr one of the next versions will also have Symfony support.
When using it, you have to remind yourself, that the php support is still far from being finished and that it still has some bugs. You can download Netbeans at http://php.netbeans.org - the latest version is 6.5 RC2.