Entries from previous years are a fantastic resource to dip into for some spontaneous gaming.
The prizes are great, but the best thing about it is an excuse to get creative and share your work with others.
If you're stuck for a map, here are three that I'm putting into the public domain. Fire up that copy of Scribus, put on a pot of coffee and get started! If you're stuck for a concept, head on over to Hill Cantons and give the Old School Module Name Generator a go. If you're stuck for the writing part, well, you're on your own. :)
EDIT: Please feel free to add comments with other usable map resources, such as the Donjon random map generator.
EDIT 2: +Dyson Logos has thrown down the motherlode with his free-for commercial use Commercial Maps list. Seriously, there's like fifty maps there!