Startup Tracker - The startup search engine 🎯
Optmyzr - Optmyzr AdWords Tools. Optimization Solutions, Quality Score Tracker, Landing Page Checker, and more. Free Trial Available.
Mattermark - Ranking 800,000+ high growth Internet companies
Freshmarketer - An all-in-one CRO suite.
The Y Combinator Database - The definitive database of YC companies with all the metrics
Crazy Egg - Through Crazy Egg's heat map and scroll map reports you can get an understanding of how your visitors engage with your website so you can boost your conversion rates.