What are the leagues that are just below the pros in basketball and football? Is it generally just college, or is there some kind of minor league system like they have in baseball and hockey?

I don't believe there is a farm system like in baseball and hockey where teams have specific teams they draw from. But I'm pretty sure the NBA teams have players under contract they can pull from the CBA and in football, they develop players in the Euro league.

Baseball's farm system is incredible... it's not something that the NFL can emulate because of the nature of the game and it's not something the NBA can do because most 18 year olds have no need for one when they can jump directly onto an NBA team... baseball's minor leagues are so deep and so important/ingrained into the game of baseball that it's tough to get your head around sometimes that some guys play entire 10 year careers in the minor leagues

Hockey's the same way.