I was at Pary City the other day and they have Princess, Cars, and Winnie the Pooh scene setters! These are huge 5 foot rolls of decorations that you put up on your walls and then you buy the additional stuff like the princesses to put on them They are so cute! I bought the Superman ones for my ds' b-day party.
I used something like that for a little kids' musical last spring. I found a plastic roll of "barn wall" at Garden Ridge in the party section. They've come a long way since paper streamers! I don't usually decorate much for my girls' birthday parties since I usually put in so much time and effort on the activities/theme. Last year dd10 had an "Amazing Race" party. This year, dd(turning 9) will have a "Treasure Hunters" party.