This is a fantastic opportunity to impress the interviewer. Ultimately, this question aims to gauge your level of interest in the company. The more you've researched prior accomplishments, company values, and basic information regarding the product or service, the more you can demonstrate a genuine desire to work there.
For instance, you might say, "I know your company is ranked the number one web design firm in Massachusetts. Your mission statement in particular appeals to me. I also know your company emphasizes continual learning and growth, two aspects I find incredibly exciting. I've spoken to Jen and Mark, two marketers at your company, and they've described the work environment as one full of passion and innovation -- which is something I hope to find in my next role."