We've experimented with automated timekeeping in our team's meetings, which I guess are "agile" or at least relatively unstructured. Everyone can see how much time everyone else has been speaking, and a little unobtrusive note pops up on your screen if you've been speaking for a long time without a break.

I think it's been good: everyone makes an extra effort not to interrupt the less outgoing people when they speak. Some outgoing people on my team commented that they didn't realize how much they dominated the conversation before. Best of all, a couple meetings don't need to happen anymore because it turns out that 1-3 people did all the talking and the others were just showing up because they thought it was expected of them.