(Updated to permalink on 24 Aug 2013)
Richard Buckle (@RichardBuckle) has written up his coding guidelines for Objective-C. IMHO they are well written and appreciate the guidance by example, along with a discussion of when he believes it is ok to bend the rules a bit. Hopefully this will be a living document and Richard can add more over time.
Like all these things, YMMV but I say thanks to Richard for sharing them.
Link: