iSmashPhone: This site contains various news articles related to the iPhone.
iCodeBlog: Various programming articles on the iPhone.
iPhoneKicks: This site is a kind of 'Digg for iPhone Programming'. It allows readers to submit links to articles on iPhone programming. These links are then voted up or voted down. The most popular links get moved to the top and the less popular ones get moved down. Lots of useful stuff here.
Mobile Orchard: Lots of articles on iPhone programming and news.
Cocoa Is My Girlfriend: Marcus S. Zarra's blog about Cocoa programming. He's also the author of the upcoming book: Core Data: Apple's API for Persisting Data under Mac OS X
Cocoa With Love: Matt Gallagher's blog on iPhone Programming.
iPhone Development Tips: Various quick tips related to XCode and iPhone Programming.
KATI: A blog on developing interfaces in Cocoa.
Planet Cocoa; Sort of a 'blog of blogs'. It contains links to articles on other blogs related to Cocoa programming.
iPhone Incubator: iPhone programming articles by an experienced iPhone programmer.
Cocoa category on Reddit: Reddit is another 'Digg-style' web site where readers submit and vote up/down articles on the web. This particular part of the site is devoted to articles about Cocoa.
iPhone Flow: More articles on iPhone development.