I know that a shvuat heses is drabanan. I think modeh b'miktzas is one, and that shvuat hashomrim is another, but what is the third? (and are the 2 I mentioned correct)
The three categories of biblically prescribed oaths are 1) an oath of a bailee ("Shevuat haShomerim"), 2) an oath to defend a partial monetary rejection ("Modeh beMiktzat"), and 3) an oath to counter a solitary witness ("Eid Echad").
See Rambam, Laws of Shevuot 11:5