One site we like is Coloring Book, it has tons of characters from cartoons, movies, etc. and 20-80ish pages per theme. I also signed up to get free samples from Dover Publishing. They make tons of books - coloring, crafts, educational, and even CDs of clip art and stuff. Every week they send me an e-mail with a link to about 20 free sample pages. I have been saving most of the jpegs and can print those off for coloring whenever the creative mood strikes us.
Our latest google search find is Coloring.com. They have a couple hundred pictures and you color them all online. You pick colors and then click on the picture, which fills in like using the paintbucket feature on Photoshop. The best part is you can save pictures, e-mail or print them, or embed them on your blog, website, etc. They give you the html code. Pretty fancy! I colored this monkey to represent Roland, Emmett helped me choose colors for the soccer boy, and Alden did the pirate ship all by himself. Then I finished off the planet scene.
This is what works for us lately. For more Works for Me Wednesday tips, check out Rocks in My Dryer.