One of my favorites is called Radio Galaxy Zoo. You're shown an image that is an overlay of radio signals on an infrared photo of a distant part of the universe. You click the picture to indicate associations between the radio signals and the infrared signals. I find it easy and calming.
Another easy and calming one involves keeping tabs on penguin populations. Basically you see a photo that may or may not have penguins in it, and if there are penguins, you click them.
This entry was originally posted at http://firecat.dreamwidth.org/861942.html, where there are comments. I prefer that you comment on Dreamwidth, but it's also OK to comment here.