Welcome aboard. Enjoy the ride.
Before we can provide any meaningful answers, we need some more information from you.
1. What kind of photography do you typically do (i.e. action, portraits, landscape, street, etc.)?
2. What is your budget?
3. What lenses do you currently own?
4. What do you want to do that you can't do well with your current camera?
You also need to understand that just upgrading to a more expensive camera will NOT make you a better photographer. The D5000 is a capable camera and if you are generally up-happy with your current photos, your time and money might be better spent on photography classes, books, tutorials, better lenses, or better accessories like flash units, tripods, post processing software, etc.