Batman and Catwoman would have to be one of my favorite couples.
Selina understands more than most that Batman is who Bruce is, because Catwoman is who she is. Neither are really able to truly escape the costumes. They can be themselves with each other and enjoy the chase, and the excitement of what they have.
And let's face it, Batman needs someone to keep him from silently brooding between Gothams gargoyles and atop grotesques.