Well, anything training a muscle below the waist can generally be considered beneficial for badminton

Upper body, you have to take care not to go too heavy and/or too slow, and incorporate lots of exercises for those pesky fast-twitch and deep muscles. Training with a swingstick (elastic stick with weights on both ends) has been proven to work deep and small back muscles WAY more effectively than regular weight training, I've been told.
Same goes for pretty much any area of the body - weight training is a very good start, but should not be the main focus. For legs, specific exercises for footwork coordination and explosive strength are more important, for the upper body, stability exercises involving fast and twisting movements are vital.
If you don't have some injury problem or specific muscle weakness, doing squats, lunges, dead-lifts, pull-ups, and benchpresses should be enough weight training.
The rest of the strength/stability training should be done with therabands, medicine balls and swingbars.
Oh, and doing drills on those pesky stability platforms (basically wobbly soft cushions). Apparently quite important for your feet/calves - not working out those muscles may result in Achilles tendon problems, as I'm experiencing right now