patch 5.1 is going to introduce a number of new pets that can be captured in vanilla zones or drop from bosses in vanilla (or originally created for vanilla) raids, such as molten core and naxxramas. along those same lines, i have a few ideas for pets that i'd like to see added in burning crusade content.
roflcopter. mechanical pet with several flying attacks. capturable. most often found around shattrath city before raid time.
shadier shade of aran. undead pet with magical attacks. drops in karazhan. its flame wreath attack does nothing unless your opponent tries to swap pets - then it blows up the battle.
image of image of archmage vargoth. magical pet. capturable in netherstorm. doesn't actually do anything in battle, just stands there.
gronn pup. humanoid pet with humanoid and beast attacks. drops in gruul's lair. grows larger during every combat round.
lil' reliquary of the lost. mechanical? undead? magic? elemental? yeah, i really don't know. wails a lot. drops in black temple.