I marinate on some garlic, black pepper and worcester sauce. Heat butter in pan until bubbling, whack steaks in, cook for about a minute each side to seal then turn the heat right down and cook for a couple of minutes each side (dpeending on the thickness of the steaks). I pour over the last of the marinade just before serving and then spoon over the top.
oh yeah, and dont mess about with it once you put it in. place it in the hot pan and then leave it be. judge how well done by watching the cooked colour change going up the sides. then when you need to turn, do the same thing.
that way you get a lovely browny golden buttery/meaty sealed outside, no matter how rare/well you want the inside.