Best tools for remote collaboration?

Our office is going to start having remote employees (all around the world), and I was wondering if anyone knew of any good remote collaboration tools?

Here's what I've found so far:

- Always-on Skype video chat, using dedicated Mac Minis

- DicoLab, multiple mice on a single computer, works remotely

- Dropbox, Google Docs, Basecamp, Trello, VNC

What other tools might help with realtime remote collaboration?