I'd start with the wheel bearing, like Twichel04 said. Pull the brake pads out and then spin the wheel. Also check the brake caliper, used brake pads are thiner, so the piston is pushed out more. When you've installed new brake pads you've pushed the piston back, might be some rust or durt prevents the piston from being pushed back to create some clearence and that creates the drag.
Master cylinder and alighnment would be my last things to check.