While a theme format of top panel and bottom text with a menu about the text seems like the default choice these days, we would entertain creative departures from the standard with extra interest.
We are hoping to avoid having to code a WP theme when so many good and mostly bug free themes are out there. We wish to get a good graphic design that a designer could integrate with an existing WP theme. No doubt, there would be some tweaking, which we shall have to take care of. That would mean having to continue to work with the winning designer after the contest is over as we finish the integration. So, perhaps the primary objective for us is to find a designer who will work with us.
Please avoid overly "post-modern" styles, as well as more complex, baroque / byzantine / curlicued / cute styles. "Sleek" and "Corporate" are, in my view, other terms to indicate what to avoid. Avoid marketing conotations.