In terms of CDs I think the Amnesty Is Granted promo or the Because Of You Promo are the rarest, they're certainly the two I've seen least of over the last few years.
As for vinyl rarities probably the CHSIB album for 12" and the 7" vinyl is more than likely the early 70's More Than You Deserve, although the Surfs Up master acetate pressing I've got possibly rates up there as well
