Stop wondering and check out this Action Guide List [voterx]. For any level of commitment (cleverly labeled: on your ass, part timer, political guerilla), there's a way to get involved.
The election is less than forty days from today (with voter registration deadlines rapidly approaching) and I don't think that Bush is going to move out of the White House of his own accord. Take a look at the list and find a way to help.
On top of putting together this nifty guide, there are plenty of concert type events going on all over the place. For instance, I'll be helping out at the Rilo Kiley show tonight at Neumo's (which is how I found the list in the first place).