Battlefield 3 Obscure Dogtags

Solution 1:

Doctor Pepper Promotional Tags:

• 6 wolf moon
• Bye Kitty
• Opener
• Roar
• Pile O Bones

This promotion ends on 12/31, and it might already be difficult to find the specially marked Doctor Peppers for this, so if you want these, act fast :)

Pre-Order bonuses:

• Ace of Spades
• Bringer of Death
• Cause of Death
• More Dinosaurs
• Haggard
• Mayan
• Yarrr

For these, you have to have pre-ordered the game. I think some of these were retailer exclusive. It seems like at least Ace of Spades and More Dinosaurs were from Amazon.

There's a full list of all the tags and how to unlock them on this site.