This one is a blog that contains free tutorials and guides for mobile development as well as comprehensive learning programs that can be purchased.
iOS Dev Center
This resource is only accessible to paid members of Apple's Developer Program and is the official iOS Dev Center.
This site offers a monthly subscription to really good courses that take you from a beginner to a pro level.
This is a forum and a really good place to ask questions and get answers from the community. Apart from app development, the forum also focuses on app marketing.
Tutorialspoint – iOS Application Development
Tutorialspoint has a really good course on developing iOS app and caters to both beginner devs as well as those with experience.
Introduction to Apple iOS App Development
Apple's official into module is a simple step-by-step guide to all a developer needs to know about developing an iOS app.
This website is part of the Envato network (the guys who bring you themeforest and graphicriver) and is a really good design & development resource.
This is a really good blog for iOS devs focused especially on game development.