Since our house number is a little difficult to see, I made a huge bat symbol to put on the front door so everybody would know what house was having the party and it worked like a charm. Every kid was yelling at their Mom while in the car "Look at his front door!" I took a piece of yellow posterboard and used a projector to get the bat symbol onto it and then painted it in with black craft paint. Very easy. It's now on his wall above his bed.
We had face painting for the kids, but only two took us up on it. One had a bat and the other kid (who belonged to me) went as the Joker:
This is his action pose
The house was filled with blue, green and black crepe paper streamers as well as the same color balloons. We also made some bats before hand for a game that the kids played. We taped them to the kids' backs and they had a game of tag where they had to chase each other (in the house - total chaos) and see how many bats they could collect.
I also had all the kids "capture" The Joker by putting him into a chair and wrapping him up with rolls of toilet paper. In order to get his presents he had to "escape" from his bonds. He loved that part.
The only other game we had was one called "Stomp the Bad Guy". We filled balloons with candy, blew them up and drew stuff to represent the bad guys on them with a sharpie marker. For the Joker we wrote "Ha Ha Ha". The Penguin had an umbrella, Catwoman a cat and the Riddler had question marks. There were two balloons for each kid to pop. One little girl was so tiny that she had to get a pair of scissors to pop her balloon. She just didn't have the weight to do it. It was very cute.
The capes that I made were also a big hit and they wore them for most of the party and were really excited that they got to take them home. They took the bats from the tag game home as well.
The little guy had this smile on his face the entire day, long after the kids went home. I call that a big success!