Drupal does not have any official merchandise; however since the Druplicon logo is licensed under the GNU GPL some people have taken it upon themselves to make their own.
FAQs about the use of the Druplicon:
Anyone can use the logo and alter it, right?
-- Yes, anyone can use the logo and alter it as they see fit.
What if they want to use the Druplicon to create a money making thing like a T-shirt or Toy?
-- Totally fine to do.
Does the profit making company need to give a certain % or royalty to the Drupal Association?
-- It'd be nice, but no.
Profits should be donated back to the Drupal project; bear in mind that Cafe Press, Zazzle and Spreadshirt do take a significant portion of the price. If you have printable iron on transfers handy consider grabbing a high resolution Druplicon and making a donation.
Basic Druplicon
Designed by Michael Angeles
High resolution versions are availiable.
The Drupal Association Store includes t-shirts too and proceeds go to Drupal.org improvements, maintenance, and community programs.
Revelinux promote Open Source projects including Drupal. 100% of the profit will go to those specific developers. They have a US Store and an EU Store.