well i use vi, but if i have to use gui i use kwrite.
Best PHP Editor for Linux?
Quanta Plus has a nice GUI for coding with a great set of features.
http://quanta.sourceforge.net/
I'm looking for something like that with CVS support.
bluefish is what I use (GUI editor).
http://bluefish.openoffice.nl/
works well for me, but I do tend to swicth between vim and bluefish.
Vim for everything!!
Vim is (apparently) good, but rather difficult and not GUI. I use QuantaPlus for KDE. This is a good GUI which supports highlighting for multiple document types.
WebRuss: Your wait is over.
Emacs, yes its is a great editor. 
Although I will admit the learning curve is high. Emacs uses strange key combinations to open files etc. ,
C-x C-f open file
C-x C-c exits program
however, if you are doing just the X-Windows gui, you can use the pulldown menu.
So try emacs...
Down with the communist pig dogs that use VIM 
.
Comparison of several editors:
Quanta works for me.
i've just discovered zend studio as being really good. though the free version has some limitations in comparison to the full studio 2.5 it really is the best i've been coding with.