I LOVE giving / receiving the gift of stationary, and one of my favorite places (esp for kids), is Tiny Prints.

Thank You cards make a great gift for everyone, because they are thoughtful (can be personalized) and useful - which in my mind, is the perfect combo!  Pictured above is an example of a baby girl thank you card.  20 cards are around $30.  

Here is an example of a baby boy/neutral thank you card:

Check them out at:  http://www.tinyprints.com