In a previous job of mine, we would show candidates a printout of some buggy code, and ask them to find the bugs. We would leave the room and let the candidate work through it on their own. The code in question was basic algorithms and data structure stuff in C++, such as inserting into a doubly-linked list. I always thought it was a good exercise. Suits slow-thinkers and nervous people, and it's a good test of coding ability since if you can spot a bug then you can clearly read and understand the code.