productboard - Beautiful and powerful product management.
Froged - One click solution providing easy-to-use marketing, sales and support services to turn website visitors into happy customers.
ProdPad - ProdPad helps your team gather ideas, surface the best ones and turn them into product specs, and then put it all on a product roadmap.
Keep Your Friends Close - A free e-book about maximizing Customer Lifetime Value
ProductPlan - Cloud-based product roadmap software solution
Intercom on Customer Engagement - A book on how to create messages that drive engagement