If you have a close-knit team and are looking to bring in a new player, it's obviously important to make sure you know who you're bringing in. I like to ask a few totally non work-related questions to open honest communication. "What's your favorite movie?" and "Why?" This give surprising insight into a persons values and interests. It also lets you know if they are deep thinkers. If the answer is, "Saving Private Ryan." that may tell you something. If the answer to the why is, "'Cause stuff blows up." you know something more about the person. Two others that are good for opening up free-flowing communication: "What does a perfect Saturday look like to you?" (this gives great insight into what's important to a potential hire) and "What makes you angry?" (the answers here vary, but you can see the candidates willingness broach the negative side of life and how he/she deals with it.)
One more for the road: I like to give a scenario applicable to the position that implies the candidate may be asked to lie at times by their manager if they are hired, and see how they respond. This can be a deal breaker. If someone will lie for you, they will lie to you.