There are random items hidden around the site (on the landing pages and in the forums). You have to collect a list of specific items for each of the 3 prizes. After you click the first item, you'll be told what else you need to get. Here's what you will receive...
-Sims 3 Ambitions Fireman - Add to Wishlist
"Reduce the risk of dying from spontaneous human combustion with the help of this axe-wielding fireman."
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- Sims 3 Ambitions Tattoo Artist - Add to Wishlist
"Get inked (or hepatitis) from this sultry tattoo artist."
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- Sims 3 Ambitions Doctor - Add to Wishlist
"There's nothing more reassuring than having a doctor stand behind you holding a large syringe."
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CGI - Complete Gaian Itemlist
Organized listing of all items available on Gaia.