Maker Swipe File - 100+ high-performing Tweets to help you grow your audience
Userfront - Know thy startup: metrics & triggers for growth
Narrow - Narrow helps you build a targeted audience and increase your influence on twitter.
Analytics Pack - A curated directory of the best startup metrics
Tweetflick - Save, organize & find Tweets to get the most out of Twitter
Growth Hacker Marketing - Ryan Holiday's book, re-released and expanded