Any competitive content would be ok I think. The real draw would be in the prizes.
While you could offer sitepoint merchandise, an even bigger draw would be commercial products such as an MSDN subscription, a commercial MySQL license, a Photoship license, or whatever fits the contest. If it’s a logo design contest, then obviously a photoshop license would be in order.
With the cost of these prizes though you’d have to ensure a quality contest. One that would not only inspire and challenge, but one where the end result would be actively used somewhere. Nobody wants to design something just to have it fall into obscurity.
I’d love to see “Design Redux” competitions, where a random, fairly popular website is chosen every month, and users work together to redesign it and code the client side in the best way possible. The idea stems from the popular design redux’s that Andy Rutledge performs on his blog.
Someone already some something similar, about charities, but how about we accessify university web sites?
I would never be surprised to hear a Facebook app doesn’t work with keyboard— that’s typical. Special commercial software? What can you do but wait on them to fix it, since it’s closed source? But college/university web sites… that’s open code. Anyone can make it better, if the school agreed to it.