Learn C on the Macintosh is a good book on the topic. While most of the Mac OS X specific stuff is just based around Xcode and there's not a lot else directly related to the Mac in this book, it's still a good learning text. Expect a full review of this text to be on iDevGame sometime [hopefully soon].

There are too many sites to even consider listing for C. If people have their favorite add them to thread. I don't even remember what I first used to learn C, so I'm not a lot of help here outside of the texts that are on my selves.