I am also a big fan of small steam engines. I own two of the recent 3rd Rail SP switchers. They are fantastic engines. My only complaint is the lack of a working coupler on the front of the locomotive. Thankfully, I operate two rail equipment, so I only have to retrofit a Kadee coupler, not the larger tinplate coupler. Considering even Lionel puts front couplers on their steam switchers, I was hoping for more, but beggars can't be choosers.
As far as wishlist locomotives (the point of this thread), anything Lackawanna (DL&W) or a re-run of SP Pacifics with skyline casings. A diesel switcher, such as an Alco S-2 would be fantastic.