One of the birthday parties I had for my kids that was the most fun was the Pirate Party! We got refrigerator boxes from a local appliance store, cut open the top and painted pirate ships on the sides. We divided the kids into groups of two and gave them cheap plastic golf balls (like wiffle balls they were hollow on the inside) spray painted black to use as cannon balls to hurl at each other's ships. We counted how many ended up in each ship at the end of a certain amount of time and the team with the most had to "walk the plank", a balance beam we had made that we placed in between the two ships. We also had a treasure hunt with riddles and an oversize map that my husband ran through with the kdis and they all worked together to solve the riddles and run to the next clue. We hung fishing net from the shrubs with fish and shells stuck in it and paper parrots from the trees.
I'm a big fan of 'mood' music, so I sea and pirate songs (thanks, Captain Bogg and Salty--Scurvy!) playing loudly in the background during the whole party. Aside from Mojo Nixon Pirate Radio, here was one of my favorites (I found a program that allowed me to silence impolite words):