What do you think Ted's patronus is?
Is there any evidence that he could cast one? I don't have my books on me so I can't go look at that scene, but I'd say that he probably couldn't. It's a very complex and advanced spell and no Death Eaters bar Snape could cast one, which sort of makes me think it's not something usually taught at Hogwarts (I find it odd that no Death Eaters ever took NEWT level Defence Against the Dark Arts, which I'm presuming the spell would come under).
If he could cast one, I think it'd be some sort of dog. We don't know much about Ted Tonks, except that he's a bit of a slob, and I'm inclined to think that he's a bit of a Jack-the-lad type character, a fairly standard bloke with a decent sense of humour. A down-to-earth kinda guy. Somehow, dog just seems to fit. Though, a Patronus is something that the caster sees as protection. Ted could have owned a pet dog when he was younger and so sees that as protecting. I don't think it'd be something overly elegant or extravagant.