Centers are a staple in my school library and I'm always looking for activities require minimal setup. I usually have the interactive whiteboard open for center use and I love that it allows students to work collaboratively. The strategy games available on ABCYA.com were especially popular this year.
40x Escape, Sugar, Sugar, and Thanksgiving Challenge all require students to use logic and critical thinking to solve problems. It is so fun to hear students thinking out loud as they work together to advance to the next level. I tried to help make sure students gave hints rather than spoilers when friends were stuck on a problem. Some of the levels on 40x Escape are so tricky that passing adults stopped to join in the fun.