While a student at UC Berkeley, Roland Saekow had the idea for a tool that would help people visualize history--all the way from the big bang to yesterday--and zoom in on whatever parts interest them. Called ChronoZoom, it's kind of like Google Maps for the fourth dimension, and it will get richer and richer as it's fleshed out wiki-style. Here Saekow demonstrates:

Microsoft Research has gotten involved in ChronoZoom. The good news is that this will presumably accelerate the project. The bad news is that if you watch Microsoft's version of the demo you have to listen to the kind of music that plays when you're installing a new version of Windows. I'll let you decide whether this is a price worth paying:

[Update, 3/25, 8:40 p.m.: Underpuppy--a commenter who is presumably the offspring of an underdog--points out that the ChronoZoom beta is available for your inspection. A quick perusal suggests that there are plenty of blank spaces to be filled in. Get to work, wiki-world!]