One of my favorite projects in MAKE magazine is Alex Andon's pet jellyfish tank from Vol 27. It's not hard to make, but people who don't want to build a tank on their own should look into Alex's Desktop Jellyfish Tank. It's a Kickstarter project with a $3,000 goal, but so far almost $80,000 has been pledged. If you place $350 or more you get a desktop jellyfish tank and starter kit.
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. His new book is Maker Dad: Lunch Box Guitars, Antigravity Jars, and 22 Other Incredibly Cool Father-Daughter DIY Projects