For past few months I (along with my awesome crew at Bombayworks ) have been developing native iPhone app for a photo listing company somewhat similar to Flickr (Sorry, I can't disclose the name).

Here is a short list that may help you learn more about iOS development. I will keep adding more to this as and when I come across more interesting stuffs.

• Ray Wenderlich - Great community for iOS tutorials and example projects. If not sure where to start check this categorized list of tutorials.
• objc.io/ - Nice periodical about best practices and advance techniques in objective C.
• Complete iOS Style Guide