Well for SR I know it's not a PrC but monk levels would work, or expensive SR-bestowing magic items. There is a shield (mirror shield?) that has spell turning capabilities. Offhand I cannot think of a single PrC that is devoted towards making someone resistant to magic/magical effects. I'm sure there has gotta be one out there somewhere, although I doubt whether it would be in a WotC book - perhaps 3rd party PrC books? I have a pretty comprehensive 3rd party PrC book, just not with me here (I'm at work) but I will look at it when I get home and see if something comes up.
I know there is that one, I think called the Forsaker (?) where you cannot use magic/magic items, and in fact have to destroy magic items like every day to keep your PrC bonuses... but IMHO that class would be incredibly hard to play, and likely would be killed off sooner rather than later. Reminds me of the Frenzied Berserker - sounds cool as hell, until you see how fast one gets taken out.