I like Mountain Project sitting at my desk but physical guidebooks lend themselves well to the half hiking involved in most climbing expeditions (despite the weight of a physical book). There's just something about being able to tick off routes and hold the book upside down to orient yourself that I don't think translates well to an app still. The book writers seem to put more effort into good maps and diagrams too.

They're fascinating, for a good utilitarian example check out The Dixie Caggers Atlas by Chris Watford. For pure art Southern Nevada Bouldering is just beautiful. I'm sure others may have some good recommendations.