Oooohhhh....Loved the idea for this challenge! I do have difficulty leaving white space, so thought this would be a good challenge to enter.
I used "Zappy Birthday" for my card, and quite like how it turned out. I confess all the white space was kind of bothering me, though (sigh--just couldn't leave it alone), so I added a strip of washi tape to the bottom edge, and then stamped the zig-zag above the row of white "thing-me-bobs"... What do you call those..."star bursts"?? I also popped up the main image on some dimensional squares, for some added "POW"! (I wish this stamp set also included a "Pow!", and a "Bam!" They would have been fun stamps to put in the star-bubble, too.)
All stamps and card stock are PTI. Thanks for looking!
And here's a close up of the dimension.