TextMate

I cannot recommend TextMate enough. At first glance it looks like a simple text editor, and if you want it to be it is, but it’s power lies in the bundles. There are bundles for everything. Want to send the file you’re working on to GitHub? Done. Need help writing a tumblr theme? Done. I can’t comment on too many of the more advanced features (I only really use it to write python code and notes in markdown), but I can say that the auto-indent for Python is a huge time saver.