Harrington and Richardson, I believe make a good economical one. Thompson Center makes a very nice one. Good thing about these are you can buy interchangeable barrels for other calibers or shotgun.
Nothing wrong with a single shot they tend to be accurate and make you a more accurate shooter/hunter as you tend to be more critical regarding shot placement when you know you likely have one shot. Though with practice you can reload pretty quickly.
Others have offered up a sighting of roughly 2 inches high at 100 yards as a good sighting scheme. In my own experience I have come to favor a sighting of 3.5 inches high at 100 yards. This allows for the individual to hold dead-on (directly in the middle of the top and bottom) the animal out to roughly 350 yards.
Magnum calibers such as the 7mm Remington and 300 Winchester will extend this slightly. At 400 yards I hold directly on the backbone of the animal. The drop at this range allows the...