In the Western world, your bank and credit card company are obvious places to start. They control your access to funds, and have an awful lot of data about you and your relationships. This is one of the major reasons the finance industry is so heavily regulated: we've collectively outsourced the enforcement of trustworthiness to the government. When government starts "streamlining" the rules to make things easier for the banks, we get things like the GFC. Regulations aren't meant to make things easy for the industry being regulated, they're meant to limit the power exercised by that industry.
For many people, this list also includes PayPal, and they're very careful to skirt the rules that would bring them under the full force of financial regulations.