I use mostly open source or free as in beer development tools on OS X, Windows, and Linux (with a major exception of IntelliJ – a bit expensive, but really worth it). There are two commercial utilities that I use almost constantly: TextPad (Windows) and TextMate (OS X). Both editors are well integrated into their host operating systems, offer good shell support, etc. On Linux, I find gedit fairly handy, but I would spend some money to get a TextPad or TextMate type product with no hesitation.