Um, I tried mid Lulu once! I would only recommend doing it if the rest of your team composition allows for it. Although I built decently, by the time mid and late game rolled around, I just didn't have enough damage to cause much of a fuss as some other AP casters might.
Diana and Nidalee top, especially on purple side, is a hoot because of spears, and the curve of Diana's Q. It's basically poke for days. Nidalee will take on more of a support role, healing and hucking spears.
I tried Syndra support, once, thinking that her CC would allow her to at least kinda do well in the role, but it doesn't really help your adc when you're picking up their last hits and throwing them away.