Mac OS X: Kod is a simple and free OS X text editor geared toward programmers that offers easy navigation and terminal integration.
Kod is in its early stages and not yet feature-rich, but it's nonetheless very promising. Currently it offers file system navigation via the sidebar and tabbed windows for better organisation. It'll also create a symbolic link for you so you can quickly access it when you're in the terminal.
While there currently isn't syntax highlighting or any fancy features, Kod feels a lot like a stripped down version of the popular but expensive ($40) TextMate. It's bound to have more features added in the future, so if you're looking for a solid text editor for programming it's worth keeping an eye on.