QuickCursor brings your favorite text editor to any app with a global keyboard shortcut. Unlike manually copying and pasting between apps, QuickCursor automates the entire process to save you time.
This app is just all kinds of awesome, and works with nearly everything (including, for example, comment fields in web pages). I love it. (Realize though that every time you save within your editor the system clipboard is overwritten, and that you can't edit in an app that doesn't support the ODB Editor protocol.)