There is a new book soon to be released for Sit 'n Go strategy by Timoth Neil. You can order it from the
SitNGoTraining.com Bookstore. Here's the product description:

Sit ‘n’ Gos are one-table tournaments, where the first three players split the prize money (50% for first, 30% for second, 20% for third), are the most popular form of online poker tournament played today. It is estimated that more than half of all Internet poker players (and many land-based cardroom players as well) regularly play Sit ‘n’ Gos. They’re quick tournaments, averaging only one hour to play, and lucrative for players who know the strategies.