Easy To Use Collaborative Editing Software?

Question

My friend and I usually don't have time to meet up in person to do some real pair programming. Since we want to program together anyway, we turned to the world of collaborative software editing.

Sadly, most of the solutions we have tried are either lackluster or don't work at all. Cloud9 (fusion of Mozilla Skywriter, ACE) is tossing errors like there's no tomorrow and makes developing a project impossible.

Notepad++'s plugin seems to be broken.

CollabEdit allows only for one file at the time. Granted, you can open multiple windows, but that makes editing a bunch of files really, really awkward and clumsy.

Is there any online or offline software to enable sane collaborative editing? We tried Skyping with a shared screen, and while it's truer to pair-programming than two people coding at once, we don't want to be limited that way.