When it comes to brainstorming, there are several personality types that I've found to all but guarantee a productive, successful, and often enjoyable process and outcome. In my experience, people who embody the following designations tend to contribute greatly to group brainstorms in the form of stimulating creativity, provoking thought, and keeping momentum going.
The Devil's Advocate
You know that person who's always challenging the status quo, voicing doubts, looking for the cracks, and generally taking a contrarian stance on every proposed idea or conclusion? That would be your textbook devil's advocate. As soon as one person contributes a thought, it affects the mindset of the entire group, prompting them to think more similarly than before.
Having someone constantly challenging you can be frustrating, but without questioning the consensus or certain ways of thinking, you miss out on the opportunities presented by a different perspective and approach to decision-making. Disputing the rest of the group's logic affords everyone a chance to look at things through a different lens, consider whether their initial ideas hold water and allow the best ones to crystalize.
The One with No Filter
Normally, when someone is described as having no filter, it's not a compliment. However, a person who speaks bluntly often says what others are thinking but won't say out loud, themselves. To be sure, not every comment or idea will be brilliant--nor is this typical or expected of any individual--but when confronted with someone who's not afraid to say whatever comes to their mind, you might find yourself thinking in unexpected and innovative directions.
The News Junkie
Current events, pop culture and other news items are some of the best wells of inspiration for timely, relevant ideas. It's so easy to get stuck in silos based on what we do, who we speak with, and what information comes our way on a daily basis. Having someone in your think tank who's plugged into what's going on, not only within your organization and industry, but with local, national and global politics, technology, entertainment, etc. can serve as a major source of inspiration.
People who proactively examine various news sources are also exposed to different points of view, bolstering their ability to think objectively, which is a huge asset when exchanging ideas with a diverse group of people.
This cross-section of personalities is invaluable to achieving great progress, and not just in brainstorming sessions; encouraging a broad mix of perspectives fosters an environment of innovation, allowing people to build on ideas and bolster each other's confidence, which then has the effect of generating more ideas. In my own company, my teams comprise these personality types and it brings a 360-degree perspective to table.
But as with any group, you can expect a certain level of friction. This can stem from a variety of factors including conflicting ideals, competing interests, professional experience, personal history, and certainly others. As a leader, balancing the opinions of different types of people is par for the course; assuming it will be a part of this process is the first step toward successfully managing it.