There are many sites concerned with the iPhone and iPad. Some are well done and some are not. Here are a few I think worth looking at:

General comment and help

• Daring Fireball
• iPhoneDevSDK
• iPhoneFAQ
• Developer Tips
• iPhone Development (Blogspot)
• icodeblog

Completely unofficial non-Apple source of apps

• Cydia

Hacks -- ways to get around the iTunes store or to jailbreak your phone

• iPhone Dev Team
• HackThatPhone
• iPhone Hacks

Stanford University has presented classes on iOS development and made videos available. This link will show you the list of lectures.