Thanks Juggy and Jantarei for the suggestion. Actually Nikon D60 has a self cleaning sensor, but it seems like its not very effective on my case. Like nas, I must be stupid that first I tried to remove the dust using the lens cleaning brush. Later I found out that I made it worst. I could see more dark spots. Then I used a blower to blow away the dirt. It worked little bit but still I can see some fine spots on my picture. Since my picture contains dark spots, I'm pretty sure that my sensor is dirty. Or does this happens because of other reason too??

Any ways it might sound stupid, but can any one tell me where is the sensor exactly? I thought the mirror is the sensor.

Juggy bro!! Its disappointing to hear that you abandoned HDR photography. I thought HDR is pretty cool form of photography. Its a great combination of photography and digital art. Any ways I would love to see your recent works. Could you provide me a link or something so that I can check out you works. Thanks and Happy Dashain to you too.