umesh, shaju, ghostrider
Most of the information required for making a good choice about which cropped sensor DSLR to buy is already available in this thread. But I guess it will take a long time to dig it out. So I will briefly list what I feel are the essentials.
Viewfinder: Among the currently available Nikon cropped sensor DSLR's only D300S,D7100,D7000 and D90 have a penta prism viewfinder. Ideally these are the models which should be considered. D3100,D3200,D5100,D5200 have smaller penta mirror viewfinders which are a pain to peer through.
Auto focusing motor: D300S,D7100,D7000,D90 have an auto focusing motor in the body. These models will auto focus with both the D and G series Nikkor lenses. D3100,D3200,D5100,D5200 are "crippled" cameras, in the sense that they don't have in built auto focusing motors. They will only auto focus with the G series lenses which have an AF system built into the lens. D series lenses generally offer better value for money because of superior build quality, better optics and lower prices.
Megapixels: Megapixels are only important if you are going to make professional quality, large sized prints for exhibition or commercial work. Otherwise 12 mega pixels is a lot of pixels.
For purchasing an entry level camera for amateur use, megapixels need not be given much importance.
Auto focusing system: D300S,D7100 have a multi-cam 3500 DX 51 point AF system. Quite similar to the multi cam 3500 FX 51 point AF system employed in all their full frame cameras (except D600). D7000 has a multi cam 4800 DX 39 point AF system, which I have personally never liked. IMO this AF system is the biggest flaw in an otherwise excellent camera. D600 employs the same AF system as D7000. All the 39 AF points are clustered tightly together in the centre of the viewfinder. Personally I find even the 51 AF points of D700 limiting, so I would definitely not be happy with a D600. D90 has a multi cam 1000 11 point AF system which is very good. The number of AF points may be less than D7000 but they seem to focus better. Canon's full frame 5D Mark 2 offers only 9 (!) AF points (which is why I would never seriously consider buying one). Canon 5D Mark 3 seems to be a superb camera on all counts. I would love to get one if I could afford the body and a few L series lenses.
ISO/Dynamic range/Latest technology: 7100,7000 both benefit from Nikon's more recent technology. I found the 7000's ISO performance, dynamic range, viewfinder clarity and LCD resolution to be far superior to that of D90/D300S. Nikon has removed the optical low pass filter in D7100 for improving the resolution. But I haven't had a chance to check out its over all image quality.
Build quality: D300S has professional quality build and manual control buttons while D7100,D7000,D90 could be termed as semi-pro.
The choice of lenses will require a separate post