Can you tell me some of the ways that foreign aid is in the best interest of the U.S.?

Nobody ever said foreign aid is altruistic -- it's not, never has been, and never will be. The purpose of foreign aid is to purchase influence in another country. That sounds evil and manipulative, but that's the way foreign policy is practiced. If you want another country to behave in a certain way, you have to make it worth their while. It's called "Pragmatism."