In just two years, Birchbox has trailblazed "discovery retail." Co-founded by Katia Beauchamp and her Harvard Business School classmate Hayley Barna, Birchbox serves its customers a monthly mix of up-and-coming beauty brands and well-established ones like Nars, Stila and Borghese, curating the experience for subscribers based on their personal preferences. And it's innovating with style: The smart packaging and design, with its hot-pink accents, make each delivery feel like even more of a treat. The latest twist? Men's products.