Hmmm, of course brownies, cookies, rice krispy treats, and cupcakes are usually ALWAYS the first to go.
However, I think having some less sugar options would be great too. Like blueberry muffins, and maybe some mini loaves of things like banana bread (YUM!), and other breads like that? I know a lot of adults that get to the school bake sale and while their kids are loading up on the good stuff they often walk away with nothing because it's always cakes and cookies and things like that.
Our church does a spaghetti dinner every year put on by the preschool (fundraiser) and the dessert table is always set up like a bake sale. The stuff always left over are things that get messy when cut (because even when you make a cake or pie, they usually cut it in slices to sell individually) because even though they might taste good they don't look appetizing. I always see a lot of coconut cake left over as well.
Hope that helps!
I'll be watching this thread as I'm getting ready to bake for the spaghetti dinner - each parent must contribute and my best friends (who had a kid in the school) HATES to bake so I told her I'd help out.