I use Araneae myself. It has code highlighting for HTML, CSS, PHP, Javascript and probably others (which I don't use). It's a very light small program but has a few minor bugs and for some bizarre reason doesn't support switching tabs with CTRL-TAB, but otherwise it s a very good program and I recommend it.
I quite like gEdit on linux, it's also very small, light and efficient. The code highlighting is easily customisable too which I like and it doesn't have any bugs - or at least I've never found any.
At the moment I use gEdit - agree with the points Ryan made above. My only problem with it is the "Find/Replace" could be improved.
When I was on Windows I always used Notepad2 - great piece of software with code highlighting for lots of languages, and every feature you'd ever want in an editor.
I tried Notepad2 a few minutes ago. But I couldn't use that at all as it doesn't support tabs. Without tabs I'd end up with 30 or so windows open at the same time!
Over the years, I've tried just about all of them, and have settled on jEdit, partly because it allows you to write powerful macros. For PHP, it does full syntax highlighting, and it's customizable.