My favorite editor in Linux is good old
Vim. It's completely text-based, but nothing else that I've tried is as fast and effective as vim. It has both syntax highlighting and code completion. Here are a couple useful links:
Comfortable PHP editing w/ VIM (which includes code completion and other cool tips)
PHP runtime syntax check (Vim Tips) (check php syntax while editing code)
Best of all, it's FREE
Enjoy!
Jon
--http://witmatix.com--