For Programmers: What resources can you offer to someone learning C?

I am starting to research the aptitudes necessary to build an iPhone App. After downloading the SDK I started going through the tutorials where I learned that the base of all the apps are the C language. While I don’t have to learn C, I feel like I probably should.

Just so you know where I am coming from: I am knowledgeable in ActionScript and basic web code (HTML, CSS, JavaScript, etc). So basically application authoring is foreign to me.

Help a brotha out!