We did the same. Shortly after my son sat the exam we had a wonderful day in London. We wanted to reward, in some way all the hard work and effort he'd put in leading up to the exam, regardless if whether he'd passed or not.
When we received his results we simply treated him to Pizza and lots of soggy hugs! (and the comical sight of his mum dancing like a loon around the kitchen, with tears flowing - you get the picture.)
We did the same. In fact we collected her from the exam, got on a train to London and took her to see Mary Poppins then stayed overnight in a London hotel - good fun! When she got her results, we took her and her brother to an early dinner - nothing expensive but it was nice. Good luck to everyone!