Ah, Patronuses. I have two favorites. Well, I do like one more than the other, but the other is still a favorite.
My second favorite is Hermione's otter. Otters are part of the weasel family. The otter represents her love for a certain Weasley. I think it's cute.
My absolute favorite is Ron's Jack Russell Terrier. I love what the Jack Russel represents. Dogs are loyal. Jack Russell's are hyper. It's a small dog, yes, but it acts like it owns the whole room. Wikipedia actually describes the dog as "sturdy, tough, and tenacious" and I think that's a great description for Ron. It also states "Jack Russells tend to be extremely intelligent, athletic, fearless, and vocal dogs." Yes, that's Ron (and before you argue that he didn't do well in school--that doesn't mean he's not smart, he's just not into it like Hermione). I think a Jack Russell would be sorted into Gryffindor. I love that a Jack Russell is Ron's Patronus.