Reading Apple's documentation was the fastest way for me to ramp up and they actually include a lot of really useful examples. Even lower level things like CoreGraphics have some in depth examples which will probably be what you need for your "Flipboard" like interactions.
Because I do so much iOS dev I have my own "library" I now use for every project. But it was cobbled together over a couple years and inspiration was taken from many open source projects.
I probably learned the most from Jeff Verkoeyen's GitHub projects, his Nimbus framework being one of the best https://github.com/jverkoey/nimbus
If you need to make web requests in your app (which basically every app should) ASIHTTPRequest is an interesting framework. https://github.com/pokeb/asi-http-request. I took the idea behind this and distilled it down to something that was much simpler which is what I needed. ASIHTTPRequest is sorta the kitchen sink of web request clients.
If you need a relational database in your app, sqlite is a simple include away. There are a lot of wrapper frameworks out there but I didn't use any of them. I wrote my first app directly accessing the C API and then wrote my own wrapper framework for it. Because I had never used SQLite before needed it in iOS it helped me learn a lot more about it.
If you need to store username/password/token/etc for the love of god don't make the novice mistake of saving to NSUserDefaults. Save to the Keychain https://github.com/reidmain/FDKeychain
One thing I'd point you to is my collection of Categories and Macros that I put into every project https://github.com/reidmain/Objective-C-Categories-and-Macro.... Specifically pay attention to FDIsNullOrEmpty, NSObject+PerformBlock, UIView+Layout. I use these categories so much that I always include them in my precompiled header file.
As a nice bonus, AFNetworking doesn't require you to implement delegates but instead allows you to use blocks, which simplifies things somewhat.
I always like talking about Objective-C and UIKit. Keeps me sharp.