#7 - July 14, 2012, 3:18 a.m.
"Most" pets are intended to be tradeable. A pet that is greyed out means that it is either in a battle slot, or has lower than 100% health. We are adding messaging for both of those situations in the next push.
All promotional, CE, Blizzard Pet Store, TCG and quest pets are currently not tradeable. All of the pets that you can catch in the game world are tradeable, as well as a massive amount of the pre-existing pets.