The early Stumpy's (83-84) and their parts are already collectible. Some of the early steel frames, a Marin Pine Mountain for example, is quite desireable. The late 90's into the early 2000s saw some of the 26" MTB technology reach it's peak and the frame and tire size go in new directions. Another example would be the early steel Salsa stems, quill or threadless, which bring better prices than their alloy cousins.