If you're on a mac and use Safari, QuickCursor (http://www.hogbaysoftware.com/products/quickcursor) is a nice free input manager that solves this problem. It lets you use a real text editor (Textmate, BBEdit, Smutron amongst others) in place of a text area. Pressing a hot key opens the text opens the text in your editor, and saving copies it back.
Sadly it doesn't yet work in Chrome, but the chrome team is working on it.