Mini pets that would be SUPER fun:
Mini parrots/kittenatoo (like the ones in that tavern in the new Lion’s Arch)
Fireflies!
Fairies
Butterflies/Dragonflies
Monkey
Storm cloud (lol)
Or something awesome like this sylvari pup: http://www.deviantart.com/art/Ferneranian-325170619
*disclaimer: I am not the artist or in any way affiliated with the above artist. I just stumbled on it and think it would be CRAZY popular as a GW2 pet.