even though I know Nolan has said he won't, I think Penguin could be done realistically. While Danny Devito's portrayal was a physically deformed maniac, there was a previous more "normal" Penguin... From his wiki bio:
Born Oswald Chesterfield Cobblepot, the Penguin is bullied as a child for his short stature, obesity, and beak-like nose. Several stories relate that he was forced as a child to always carry an umbrella by his over-protective mother, due to his father dying of pneumonia after being drenched in a downpour. These traits make him an outcast in his rich, high society family; their rejection drives him to become a criminal. In keeping with his family's tradition of wealth, the Penguin lives a life of crime, yet executes it with his own self-proclaimed class and style. In keeping with his pretensions of being a refined gentleman, he also prefers to wear formal wear such as a top hat, monocle, and tuxedo during his jobs.
The Penguin received his alias from a childhood nickname, bestowed by his peers, who teased him because of his grotesque appearance and love of birds. (Retellings of his origin suggest he also suffered from some sort of hip ailment, which caused him to waddle when he walked. The Penguin shows no signs of suffering from this affliction today.) Some comics suggest that he tried to abandon the nickname, which he hates, but it has been permanently brought into popularity by his high-profile criminal career. He has cashed in on its popularity with his Iceberg Lounge nightclub in Gotham City.That could set up an interesting story, imo. Bruce Wayne deals with him in various social circles since Penguin is in the same economic situation as him, while at the same time fighting as Batman to keep him and his minions from taking over the city's underworld from the remnants of Carmine Falcone's operation.
It could be done.