I have two options to choose from:
One, I use Strawpoll and don't allow people from the same IP to vote. This presents two problems, however. For one thing, it really is not hard to reset an IP and manipulate the votes anyway. Two, it also prevents multiple people from one household from participating in the poll (such as brothers who both use the forums).
The second option is just reset this poll as if nothing happened, but I won't allow for extensive alt rigging at all. I'm already aware of several accounts that have participated in rigging this poll and I'm keeping an eye on new accounts registered on the forums. If a user is getting enormous spikes in vote counts after low activity plus several other determining factors, that user, as well as all users who have appeared to rig the polls, will be completely disqualified from all 2015 polls.