The Games 4 Learning store at Teachers pay Teachers has a really fun set of math brain teasers. There are six in the freebie, but you can buy a full set with 54 different brain teasers.
There are lots of different ways to use these brain teasers (whole class use, individual use, stations, smartboard etc...) and Teresa shares them all.
These are questions like: Alice has two friends and they are all different ages. Determine each friends' age given a set of clues.
I may be a big dork because I would solve these for fun :).
These are recommended for 1st through 3rd grade, but I think 4th, 5th, and even 6th grade students would benefit.
Enjoy! Remember to have your colleagues download their own copy, don't worry, it is free!