Well, I occasionally pick a "Pokemon of the Day" and try to act like it the whole day... (which is hard if I pick something like Slowbro, Abra, or Snorlax) But naturally, I behave like these Pokemon:
Ninetales: I am smart and tend to be vengeful toward people who do bad things to me or my friends, or just bad things overall. People often see me as mysterious and often misunderstand me.
Banette: A lot of times, I'm very bitter towards everyone, even the innocent. I will not hesitate to hurt someone in any way, without getting in trouble that is... I feel like I was dumped and thrown away a lot.
Skitty: People are sometimes attracted by the way I look. I tend to be excited easily, and I have a weird way of showing my emotions.
Gardevoir: I seem to have a faint ability to read people's emotions. Also, I tend to protect people from harm, especially my friends.
Kecleon: I can usually blend right in with my surroundings and situations. However, some parts of me can never be changed. (the stripe on Kecleon's belly)
Bagon: I have a dream to do something no ordinary human can do, and I am so determined to do that something that I get very upset when I try to and fail. But with that, my dream has grown stronger than ever. (And, I guess I'm at the Shelgon stage already, where I am incapable of doing lots of things as I await evolution...)
I'm sure there are others, but I can't think of anyone else off the bat...