Collaboration tools

I have several collaborative projects in progress and I use several tools to make the collaborations easier. What do others use?

• Skype: number one tool. I chat weekly about two projects, and less frequently about another more free-form project. One collaborator lives less than ten miles away from me, but I work in another town and we've both got time constraints that make Skype the easy option for conversation. My other professional collaborators live a thousand miles away, so clearly Skype is best for that communication as well.
• Gchat: I have much less frequently used gmail's chat feature to work with students; somehow they're less shy that way and they don't have as much mathematical material to convey so the lack of equation support is not a big problem.
• Dropbox: best file-sharing around. It's suddenly much easier to keep one version of a working paper up to date, rather than ending up with half-edited this and semi-revised that in about 6 different pdfs. My collaborator groups store our tex files and image/bibliography/supplementary files in a group Dropbox folder and we can compile right in the folder. I love it.
• Google docs: useful for some shared notes or spreadsheets -- I use it for communicating with my students in several classes -- but useless for tex. So annoying to use. Dropbox wins.
• Wunderkit: a new task management program in beta that allows you to add people to a working group, facebook-style. I would love to try using it with a collaborator except that file-sharing might be a bit clunky or non-existent. Perhaps more such functionality will be added as it grows: I'd love to try to use it more fully as a place to leave notes on progress, make to-do lists, etc.

These things make collaboration so much easier and more workable than I found it to be in the past. I think this technology has allowed me to sustain research collaborations despite being at a small liberal arts college in the Midwest surrounded by cornfields or soybean fields or whatever it is they're growing this year. That said, I do love reading the letters between Grothendieck and Serre... wouldn't it be cool if we were still writing letters? I don't know if scraps of my pdfs will be available to future biographers, and there's so much less personal exchange in those latexed files....