I like to terrain stuff. I propose a competition to design the best possible terrain for a Starcraft world. Doesn't have to be done in the SC editor, although that would be a natural way to do it. Other acceptable media would be the Warcraft III editor (since it offers such a powerful terraining capability), or simply to draw/paint artwork. One category for each of those media: SC1 editor, WC3 editor, and artwork. To convey the entry, post screenshots if it's in an editor, in addition to the map itself (for those who can open and look at it), or just post scanned images of the artwork. Winner in each category might get perhaps 5000 gold, all entries 1000 gold.
Probably as big as you want, but the size of the overall map might have an importance (with doodads and all) so the bigger they are the more stuff they have. Interesting ideea. Though the only one that would really allow us to make a world for SC is the war 3 editor and the artwork. SC1 editor is reduced to the terrain types in it, and i don't think makeing a map in the same 3-4 worlds would be nice.