I originally did this back in 2008, and then applied this to the 2012 election. The methodology was also retroactively applied to the 2004 election using available state polls. In all three past elections, the calculation correctly predicted the winner. It also had a pretty good estimate of the number of electoral votes that each candidate ended up getting.
The approach and the website are not as fancy as 538.com but the results so far are pretty good. The methodology is explained here: http://prespredict.com/methodology.html.
It's a bit early and there are several caveats, including the accuracy of polls in the current political environment, the independence assumption in the model, the choice of the winning probability curve, etc. Since the predictions for the last three elections have been pretty accurate, I decided to leave the calculation as is, despite the presence of the caveats.
The website is automatically updated daily at 8am PST, so you can check back periodically.
