Traditional lore says sear your steak first then finish it at a lower temperature. I recently tried J. Kenji Lopez-Alt's "reverse sear" method, which saves the sear for last and liked it. Nancy Leson's approach is sear first, oven second..
First, the reverse sear only works with a thick steak — an inch and a half at least. Cook it on a rack at very low temperature until an instant read thermometer gives you the degree of doneness you're after. In the case of the steak I tried this with, medium-rare took about 40 minutes at 250 degrees. I took it out of the oven and finished it to a crusty brown with a minute or so per side in the screaming hot cast-iron skillet waiting on the stove.
The virtue of this method is that I can control the degree of doneness exactly and have a a nice crust on the steak. And unlike the traditional methods, you don't have to let the steak rest before serving. Here's Kenji's complete instructions.
Nancy Leson says the reverse sear is too time consuming unless you're doing a bunch of steaks for company. Nance says to sear first and then finish in a 425 degree oven. She says about six minutes is right for an inch and a half steak to come to medium rare.
She makes a good point but I don't mind spending the extra time. I actually started my steak the day before. I salted and peppered it and put it uncovered on a rack in the fridge overnight. This allowed the salt to penetrate into the meat and also dried out the surface for a better crust when I finally did get around to searing.
Sides? Nancy likes oven fries. On the rare occasions when we have steak, I stop at McD's for a bag of fries on the way home and toss them in a hot dry wok at serving time.
"My favorite animal is steak." – Fran Lebowitz