Aside from the vehicles, it doesn't seem like anything is too difficult to find right now. At the beginning, the deluxes (Indy w/horse and Germans w/motorcycle) were nowhere to be found - but I've seen them a few times the past couple weeks. Our local Target actually was stocked to the gills with basic, deluxe, and Adventure Heroes yesterday when I stopped there - and had 2-3 each of the aforementioned deluxe packs.
As far as overall pegwarmers, I think I'd offer the same ones mentioned. For deluxe, it seems to be (somewhat surprisingly) the Indy w/Ark figure, although most of the others aren't too tough to find either. For the basic line, probably Mutt Williams (the shirt one in particular) although none have been too overly difficult to grab. I'd say that Marion, Irina, and the Cemetary Warrior seem to be the most difficult to find.