Maker Swipe File - 100+ high-performing Tweets to help you grow your audience
100 in 100 Challenge - Get 100 new paid users in 100 days
Narrow - Narrow helps you build a targeted audience and increase your influence on twitter.
GrowthHackList - 100+ curated growth hacks for makers + early stage startups
Tweetflick - Save, organize & find Tweets to get the most out of Twitter
Marketing Examples - A gallery of real world marketing case studies. Updated every day.