If you live in California, and you haven't registered to vote yet, you can do it now, online.
Note to 17-year olds: if you're going to turn 18 by the time of the election on November 4th, you can register to vote for it now.
Here's one reason you should: the Secretary of State race...
The state-level "Secretary of State" is typically the chief elections officer, the office in charge of many of the details of actually running an election.
If you want to see the kind of damage a bad Secretary of State can do, look at the recent history of Ohio. In 2004, the Republican Ken Blackwell played lots of fun games like shorting Democratic districts of voting machines, leading to long lines that lasted on into the night, going out the door and around the block in the rain. The voters then elected a Democrat, but I guess things got too boring for them, so in 2011 they elected another fun Republican: Jon Husted. He's brought the excitement back to Ohio politics, fighting the good fight against early voting (being able to vote on a Sunday is sacrilegious, particularly if Black churches offer shuttle buses so their members can vote after services). Unfortunatey, those killjoys at the dailykos have endorsed the Democratic challenger Nina Turner for Ohio Secretary of State.
But my point here is that (stop me if you've heard this one) the Republicans really suck, and if you put them in charge of enforcing the rules, they'll cheat as much as they can get away with (and sometimes more). There's nothing magic about Brand D, and it's entirely possible that some day we'll see a return to the days of democratic machines rigging elections, but at present that all seems like ancient history. If there's one office you don't want held by a Republican-- actually, there's probably way more than one-- it's the Secretary of State office.
Here in California, the Democrat Debra Bowen has done a fantastic job as Secretary of State. When she took over from the Republicans in 2006, the moment she was in office, she took aim at the worst of the electronic voting machines, which look like they were designed for election rigging. Now, she's up against term limits and has to step down.
The CA Secretary of State seat is up for grabs, and unfortunately the Republican Pete Peterson seems to have a strong lead, or he did in the one pre-election poll conducted six months ago. But that poll showed a huge chunk of undecideds (over 40%), and California is a heavily Democratic state, so with a good enough turn-out, the Democrat Alex Padilla may yet win this one.
If you'd like to contribute to Alex Padilla's campaign, such things are possible over at Actblue.
Also, the dailykos has endorsements for a number of other Secretary of State races.