Ivan, this is what I was too lazy to write last night...
1.) Go read
this article by Magnatique, particularly part 4 - The Design. It'll give you good ideas on how/where to integrate the ads for your sponsors and the thumbnails on the page.
2.) Go to whatever TGPs you'll be submitting to and checkout the first 10 galleries listed. That'll give you a sense of what types of galleries they list and soon you'll start to notice the difference between good galleries, average galleries, and bad galleries.
3.) Look at everything from the surfer's point of view. What's the first thing that catches your attention when you view the gallery? In the gallery above it's the THUMBS because you're using really nice content - but that won't make you money. You want the first thing they notice to be your ADVERTISEMENT. That's not to say you should bury the thumbs at the bottom of the page under a full-page ad, just that you should work text & graphics relating to your sponsor into the gallery as well. (Standard 468x60 banners won't do the trick.)
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Plenty of wheat to go around.