Sometimes the best ideas are the simplest. Case in point: Drop Stop. This cushion for car seat gaps may seem unremarkable at first glance, but it's proven incredibly lucrative for its two creators and one savvy investor.

When entrepreneurs Marc Newburger and Jeffrey Simon appeared in the tank to pitch the concept in 2013, the idea was good enough to get Shark Lori Greiner signed on as an investor. Now, with her crucial guidance (and cash), the company is growing larger than ever.

Just five months after Drop Stop's appearance on Shark Tank, the duo amassed over $5 million in sales. And thanks to a cushy multi-million dollar deal with retail giant Walmart, Drop Stop's reach has spread nationwide, guaranteeing this safety product will wedge its way into the hearts and seat gaps of many more drivers.