The Australian monos are stupidly rare and well worth hunting for if you get the chance. There are also a number of Australian publications and contributions to both D&D and the RPG world in general over the past 30 years, a number of which do not surface too often and are both worth money and worthy of adding to your collection or someone else's.

I'll leave it to other more informed collectors to chime in with specifics, but the monos, Ysgarth and a number to 'zines and tournament dungeons come readily to mind.