Someone asked me to answer this, so I'll just toss our hat in the ring as well. Our online community platform https://answercart.com can be used for that purpose. Some things you'll want to consider when making your choice:
Do you want a hosted application or do you need software you can install (our platform is hosted only)
What's your budget, do you want a monthly fee for service or a flat rate
Do you need to tie into another existing platform (like a shopping cart or blog)
What's your experience level and your staffing resources to run the system and how user-friendly is the platform?
Do you need to have censor tools or moderation features (will you be sharing mod responsibilities among several people)
What type of customer support do you prefer?
Do you have an existing website that you want to tie the new Q&A community into? Do you want the community embedded within the existing site?
Do you need to import data from an existing community?