@behoove_me
I was talking about some professional cameras with full frame sensors. Thanks for your suggestions. I will definitely look into D800 and let u know any progess. 

@Rewire,
Thank you for your suggestions. Actually, I want to buy some prime lenses so thought to upgrade my camera as well. I am still learning about photography (compostions, rhythms that make pictures great), already playing enough on manual mode. I am looking to buy some pro lenses so I wanted to upgrade my camera too. D5000 doesn't have built in motor so I wanted to upgrade it. I will definitely learn about speedlights and other stuffs u talking about. Thanks again!!!

@sukuchha,

Thank you for sharing your experiences. What should i look into when buying a flash?
Thanks again!