Guardian, Standard, Metlife are 3. It's wise to consider disability insurance now, balanced with other options of things you could do with any extra $$$: Roth IRA contribution, paying toward loans, IBR, PSLF, etc.
You'll only be able to insure your resident salary, but you get the benefit of medical eval now (when you are hopefully healthy) without need for re-exam when you become attending. You want ability to buy into insuring attending salary when you finish.