A modest investment in these industry disruptors could turn into big money over the long haul. The global financial services sector is an ocean of investment opportunity, worth over $33 trillion today, and expected to grow to over $44 trillion over the next few years. But it's not an easy place to build a business. Giant banks and other incumbents wield immense power over new entrants, and that's before companies must navigate the industry's regulatory hurdles. That said, some companies have gotten a foot i ...