As Americans head to the polls today, they should program one very important number into their cell phones: 1-866-OUR-VOTE. If you encounter any suspicious situations at the polls, log them at that number, and help citizen activists patrol the vote.
Several web sites are publicizing voting irregularities as they come up, including protectourvotes.org and talkingpointsmemo.com.
Finally, electiononline.org has a good rundown of voting news broken down by state.
Update: People keep mentioning more sites monitoring voting incidents and problems around the nation. Other good ones include electionprotection365.org and votetrustUSA.org.