I am having a bigger shower that my Mom and Sister primarily put together... I have 3 other people who contributed somehow (plates/napkins, cake, muffins, etc)
I found manicure sets ($8 at Kohls) for everyone and for my mom and sister I got them a gift certificate for a mani-pedi at a local salon they go to ($30). I figured they deserved a bit of pampering after all of their hard work.
My thank you note is super cheesy/cute and says " 'Mani' Thanks for all you've done!" with a personal note of appreciation inside.