Tools for Geographically Distributed Software Development is a good article about some of the software tools you can use for developing software with developers spread over the world.
I've worked in a few geographically diverse projects, in one of them we used Google Mail, Google Chat and Trac. In one of the others we used JotSpot and Campfire.
There were things I liked and didn't like about these tools, I liked the speed of Google Chat, but wished it was more like a Campfire chatroom, where more people could come and interact together. I didn't like how slow Campfire was, and that it put these big "sness has entered the room" and "sness has left the room" messages right in the conversation flow, but I did like how it let you see the history of the conversations of the day.
I loved Trac, and will use it in the future. Jotspot, not so much, it has a lot of features, but was slow as molasses and just didn't feel fun to use.
