Live Earth is today, taking place in 9 different locations. Since I'm pretty sure even the most motivated person could only manage to show up to two of them, it makes the most sense to watch from home (saves carbon too!). MSN has a whole page devoted to it with live streams of the different shows.

A couple of the headlines if you haven't been paying attention:
Live earth will have shows on July 7th in nine different cities: Sydney, Tokyo, Johannesburg, Shanghai, Hamburg, Rio de Janeiro, New York (well, not quite), some place in Antarctica, and a newly added show in Washington, DC; Bad Timing: On Wednesday Gore's kid was caught speeding (in a Prius of course) and with drugs; Don't cancel! It'll mess up the seven continents thing! Rio Live Earth show in question, then secured; PETA, Muse's Matthew Bellamy, and a Congressman have some troubles with Live Earth; And Madonna has invited a member of Gogol Bordello to play with her on stage