Having employed people in the past I can feel your pain :) and a lot of candidates can't provide too much in way of meaningful code. I found that small tests mainly in the realms of problem solving worked the best. Nothing to hard but enough to test their approach in problem solving. You could also provide them with some code that doesn't work and ask them to debug, again nothing too hard but just enough to challenge them. Competancy based questions / interviewing techniques can also give you a good insight into the potential employee but don't rely soley on these.