in no particular order, some threads to see:
http://www.cakecentral.com/cake-decorating-ftopict-22980-hamburger.html
http://www.cakecentral.com/cake-decorating-ftopict-12422-hamburger.html
http://www.cakecentral.com/cake-decorating-ftopict-46941-hamburger.html
http://www.cakecentral.com/cake-decorating-ftopict-36075-hamburger.html
http://www.cakecentral.com/cake-decorating-ftopict-28871-hamburger.html
http://www.cakecentral.com/cake-decorating-ftopict-29147-hamburger.html
http://www.cakecentral.com/cake-decorating-ftopict-5243-hamburger.html
http://www.cakecentral.com/cake-decorating-ftopict-216711-hamburger.html
http://www.cakecentral.com/cake-decorating-ftopict-184001-hamburger.html
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basically -- 3 layers of cake (tho' I REALLY like the idea of the "meat" being a brownie!!)
and then additions of fondant for cheese, lettuce, onions, tomatoes and buttercream for the ketchup and mustard.
I just came across this site today and happened to be on AllRecipes earlier and one of the photos of the day was the hamburger cake. Try looking there they had alot of great photos and reviews.
Good luck
The decopac website has great instructions for one with a plastic spongebob on top - it's in their most recent newsletter
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