Forgot to add:
In terms of posture, you want exercises that will bring the shoulder blades back and together. (various rows, for example) Bring your belly button towards your spine with a solid ab routine and pull the shoulders back by adding some muscle fibers up there, and you'll naturally have good posture. When those areas are weak, you will slouch.
Targeting the erector spinae with goodmornings, bent over rows and hyper-extensions will do a world of wonders, too.