since you're a stay puft fan, there are several cool things that i've seen on there in the past few months. probably the coolest, and a one of a kind
, was an ORIGINAL stay puft hand from the original latex foam costume. it went for like $380, and i was outbid at the LAST second. :l( another cool stay puft peice, still one of a kind, was the ORIGINAL final design drawing, it went for like $350, but didn't hit the reserve. i came VERY close to buying it, and i still might get my paws on it. another cool thing, more merchandise than production material, would be the tsuduka stay puft model, brings a pretty penny on ebay. i think the scale is like 1/90 or something. i THINK it's about a foot and a half tall. it came with two heads, happy and angry. tsuduka also produced a fine terror dog model, which i own. right now, i have more terror dog peices in my collection than stay puft. there are also animation cels from the stay puft RGB episodes, some for as cheap as $25. more common items are the RGB stay puft figure, probably $25-50 MOC.
as for what i collect, ANY production material from either GB film. my favs are concept drawings/paintings, storyboards, character designs, scripts, props, etc.
good luck! shoot me an email sometime.