Early on in my restaurant career, I was taught to judge a steak's done-ness by touching the meat with my fore- and middle fingers and comparing the softness with the softness of different regions of my lower anatomy.
- Rare - should be as soft as your butt cheek (gluteus maximus).
- Medium - should be a little more firm, like the back of your thigh muscles (hamstring)
- Well - should be firm like the muscles on your calf.
I was taught this method by a very well respected and knowledgeable chef