D90...
o many more things that you can do with it.
You can use more lenses as it has the Auto Focus motor thingy built in, therefore meaning that the lenses don't have to have the motor to be Auto-Focusing.
It has TWO comand dials, one for the thumb, and one for the shutter finger, allowing you to change Aperture, and Shutter speed when in manual mode by simply rotating a dial.
Has movie mode. now.. don't think that this will take great movies.. it wont. it lacks auto focus whilst you are taking the movie ( it will focus before you start taking the movie.. just not whilst you are actually recording ).
Has a LCD screen on the top. hence saving battery power as you do need to power a energy savvy colour LCD screen. also making it VERY VERY easy to see whats going on.
The down fall is the cost. you need to weight up what you are going to use the camera for against how much money you have/want/can spend on the camera. if you are not going to be using it a great deal, then maby you don't need, nor care about the extra features mentioned above, so therefore the extra money is wasted money that you could spend on a tripod/flash/lenses. But if you are going to be using the camera quite a bit, or you wish to really get into photography, then the extra money is well worth it.
I have a D90 myself, and LOVE it. i have only just shut the shutter 1,118 times to date, and i LOVE IT !
the things above are not the only differences.. but i believe that they are the most worthy differences. that i can think of atm, and being the ones i can think of.. logic has proved that they are the most worthy.. hence why i am remembering them ( yea.. you get the idea, lol )
my .02
oh and if you are new to photography. i recommend getting one of these (see pic) to go with it. i know they make one for the D90 and D60, not sure about the D40. but i'd reckon there would be on.
this book basically replaces the user manual BUT STILL READ IT ! and also tells you about composition, lighting, lenses, flash units. Give you an insight into how to shoot in different situation, such as Action, Portraiture, Macro, etc etc.
