Saints Row: The Third is $19.99 at GMG. It activates on STEAM. I've confirmed it. Steam has it for $33.49 today. Get it cheaper for exactly the same thing.
When you buy it from GMG, on their site they will give you the key and email it to you. Just copy and paste that key in to "Activate a product on Steam" in Steam and your done. You can d/l it from Steam, runs in Steam, is as if you bought it from Steam.
Will show up as $40 in checkout cart. Put in the following voucher code to get it to $19.99. US confirmed, probably Europe, pretty sure that's were they are located.
Voucher code FIFTY-SAINT-XMASS - Voucher expires: 1000 GMT 26th December 2011