Best method to prevent gaming with anonymous votin

Question

I am about to write a voting method for my site. I want a method to stop people voting for the same thing twice. So far my thoughts have been:

• Drop a cookie once the vote is complete (susceptible to multi browser gaming)
• Log IP address per vote (this will fail in proxy / corporate environments)
• Force logins

My site is not account based as such, although it aggregates Twitter data, so there is scope for using Twitter OAuth as a means of identification.

What existing systems exist and how do they do this?

Answer 1

Different approach, just to provide an alternative:

Assuming most people know how to behave or just can't be bothered to misbehave, just retroactively clean the votes. This would also keep voting unobtrusive for the voters.

So, set cookies, log every vote and afterwards (or on a time interval?) go through the results and remove duplicates based on the cookie values, IP/UserAgent combinations etc.

I'd assume that not actively blocking multiple votes from same person keeps the usage of highly technical circumvention methods to a minimum and the results are easy to clean.

As a down side, you can't probably show the actual vote counts live on the user interface, or eyebrows will be raised when bunch of votes just happen to go missing.