For the best bang for your buck, the Nikon D80 is ideal. 10mp with full AF on all Nikon mount AF lenses.
Here's a great Ebay vendor that sells only Nikon USA imports, important for future Nikon support and repair.
http://search.stores.ebay.com/Cameta-Camera_d80_W0QQfcdZ2QQfciZ5QQfclZ4QQfromZR10QQfsnZCametaQ20CameraQQfsooZ1QQfsopZ3QQfsubZ3QQsascsZ2QQsaselZ27280321QQsbrsrtZdQQsofpZ2
Looking on my local edition of Craigslist, I found several D200's for under $900.
http://sfbay.craigslist.org/search/sss?query=d200
http://sacramento.craigslist.org/search/sss?query=d200
I love my D200, because I can use even the older manual Nikon lenses with full metering.
But a D80 will be MUCH simpler to operate as a D200 requires a great deal of photographer investment in setting the camera for the situation. The D80, like your D40, has user-friendly modes for most shots.
From your history of questions, it looks like you would really benefit from taking some photography classes. Your D40 is a capable camera.
Out of curiousity, what are you needing the 50mm lens for? Your 18-55mm kit lens covers that range and you can increase your ISO for lower light, or use an SB400 or SB600 flash for other situations.
Do you have any other lenses? If not, consider selling your D40 with the kit lens and starting afresh.
Just a thought.
Edit for a response to Anthony - I've shot with enough 50mm lens over the decades to realize the difference. But I was just asking what the questioner was intending to shoot. As a photographer, photo sales rep, and a photo class trainer, I've used a few 50mm lens in my time. If you check the profile, you'll see that the questioner has had many questions about how to use their D40. Yes, a 50mm lens is great. But does this user really want the speed or have they been given one piece of information and are reacting to it? Just trying to help here.
And if one is truly using the 50mm for selective depth of field, then manual focus will give the shooter more control over which part of the scene is in and which part is out of focus. Therefore, a 50mm used manually will work wonderfully with a D40.