Ooh, I forgot about Smeargle! Definitely a unique Pokemon. The concept behind Sketch is very interesting to me.
Swablu is also unique in the same sense as Azurill, with it losing its Normal type upon evolving.
Wigglytuff- If you've played any of the PMD2 games, you would know. Wigglytuff is amazing.
Munchlax- I loved the concept of Snorlax, I just always thought it was too...big. Muchlax is a nice size, with the same general idea as Snorlax. Perfect!
Azurill- It's just so cute! "Polka Dot Pokemon" ....How can you not love that?