Editing your theme using WebDAV in Coda for OSX

Coda is a rather nice code editing tool from Panic, which allows you to easily connect to your store, download and edit your theme files, and then re-upload them.  A free trial can be downloaded from their website at http://www.panic.com/coda/

Coda is very east to set up, and gives you an excellent editor with code highlighting built in.