Win Probability Scoring
As an alternative to ERV scoring, the Cheat's blog just did a White Sox game based on Win Probability Scoring - how much a particular player adds to a team's win probability by his performance. Here's the link. Although it's intriguing as a concept - and has been suggested by others - there are some data problems with WPA at this point. First, the data set for win probabilities may be a little off at this point. The data, as I understand it, is from 1979-1990. And, as it turns out, baseball has changed a little bit since 1990.
In addition, the WPA statistic is not terribly predictive in nature - a batter gets more WPA points if he hits a home run in the 9th inning of a 1-0 game than he does if he hits it in the 5th inning. In addition, I wonder how well it tracks the performance of a pitcher who pitches well but loses. It's interesting, and I think you'd be interested in reading the Cheat's scoring as well as the Hardball Times article linked.