When I am interviewing technical candidates, there are a few specific things that I'm looking for:
-- How will they fit in with the team? Is their personality compatible?
I first do my best to get the candidate to relax. I talk about my background, I talk about the company, I make jokes, I get them laughing, etc. I want to know how the person will be once they're settled in after 6 months and assume that, initially, they've got nerves or are on their best behavior. Once they relax a bit, I ask them to walk me through their ideal work day and probe that concept with follow-on questions for a bit. Above all, I make it as conversational as possible versus just a Q&A session.
--How are their communication skills? Can they convey a technical concept to a technical person, a technical concept to a non-technical person, etc?
I'm generally interviewing for positions on smaller teams. These teams generally need to wear multiple hats and have interactions with non-technical teams. Evaluation of this skill happens throughout the interview, especially when I'm asking them to explain projects that they've worked on. I will probe on the business and technical end of the project to get a feel for how much they understand both sides and how well they can communicate both sides.
--How likely are they to be a poisonous or negative influence? How do they handle criticism?
In my region, the IT market is pretty small. I will usually ask a 'bait' question (though I don't like it, it seems to work) here and say something along the lines of "Oh, I see you worked here, I've heard some pretty bad things about that place..." and see what their response is. I'm looking for people to handle it gracefully rather than taking the bait. In addition, as we're discussing the details of a particular project they've worked on, I will challenge them on the choices that were made to see if they can defend it and if they can take criticism of their ideas if warranted. Questions like "Why did you use Technique X instead of Technique Y?" And then probing on that front.
Problem solving skills
--Can you take a business problem and develop a technical solution to it?
This one is usually something I have to infer as I haven't been able to come up with a good set of questions. However, having a conversation about a project that they've worked on usually helps.
--Can you be passionate about something you're working on?
I usually ask people to describe to me their most favorite project that they've ever worked on. I want to see them get animated and excited about something that they've done. And then I'll probe about what made the project so awesome. Answers to those questions are insightful, e.g. "I learned new technology X", "Business Problem Y was a new vertical for me", "it was difficult and accomplishing it made me proud", etc... I will also ask about hobbies and other related things here.
--Do you actually know stuff and can you admit it when you don't?
Depending on the position, here I will ask about high-level and low-level technical concepts. I want to see how much listed on the resume is actually accurate and, contrary to the first section, I want to make you a little bit uncomfortable to see how you handle it. Also, I'm looking for you to honestly, without embarrassment, say "I don't know."
After I get through all of these things (not necessarily in this order (except Personality, which is always first)), I feel like I can make an informed decision about the quality of the candidate.