Arguably iOS 7 bring most drastic changes to iOS in last 3 to 5 years. With new features like dynamics in UIKit, (more/new) auto layout, it creates both opportunities and challenges for developers. But I know the Mac/iOS developer community is best, in terms of sharing knowledge. With the iOS 7 out just 2 weeks ago, I already see some good iOS 7 dev tutorial and guides.
Tristan O’Tierney @tristan recommend this one by @ashfurrow. Note Tristan is one of the early iOS developer for Square. Ash Furrow is an iOS developer @teehanlax.
Essential iOS 7 developers guide by Double Encore
Remember seeing those guys (guys wearing their T-shirt) at one of the iOS dev conference (Voice that matter, Fall 2010 at Philly).
RayWenderlich.com iOS 7 by tutorial
This is probably the most comprehensive and the best iOS tutorial in the market. Ray started this tradition from iOS 5 (so this is three years in a row). Note Ray has also published a few shortened version of selected tutorials in the iOS 7 tutorial feast (free).
I will add more as I see fit.