It’s amazing how much time you can spend getting your favorite editor set up correctly. jEdit runs very nicely right out of the box, but there are tons plugins and other niceties that make it something close to a full-blown IDE. The best of these is ProjectViewer, which helps you organize your work (no matter what sort of coding you do). If you’re a PHP coder, then you’ll want to check out PHPParser, which can check your code for errors and spit them out to the ErrorList. Along with that, check out TaskList, which can parse your code and extract specially-tagged comments (like FIXME, TODO, and NOTE), creating a quick way to navigate to spots in the code you want to work with (I keep these three docked along the right hand side of my window).
If you work with CSS, then the ColorChooser is nice. And, if you deal with code that requires compliling, the Console makes it’s easy to execute the necessary shell comands (these two I dock along the bottom, along with the file system browser). Add a few ProggyFonts and you’re good to go. (Well, you might also add the Background plugin, which lets you set an image behind your text–in case solid colors get boring).