I'm upgrading my Digital SLR, any suggestions and recommendations?

First of all, i have a Nikon D3100 with 18-55mm and 50mm 1.8g
i've been thinking of selling it for about $700, oh yeah BTW i've been using the camera and the lenses for about 1 and half year approx. Is it a fair price i'm selling

okay!
Now my Budget is around: $1600+$700(after selling the cam)
what's the best choice i have of upgrading
now i fully use everything manually except the white balance ( even the focus)
i've been thinking of D800 but i don't think i'm gonna find it sooner

Not being a Nikon user, I did a quick search at the B&H used store and found a D3100/18-55mm for $399 and a 50mm 1.8g for $179… So, $578.

The biggest question is why do you want to upgrade? What can a new camera body do that your current one can't? Remember… Photography is roughly 70% skill/experience, 20% lens quality, and 10% camera body.

I had my first DSLR for 7 years before I upgraded the body. By the time I upgraded the body, I had upgraded all of my lenses to f/2.8 or better.

My suggestion? Don;t upgrade!

Get some better glass or lighting gear… You'll get more bang for your buck.

You won't be able to sell your D3100 for 700$! It sells in stores, brand new WITH a kit lens, for 550$ for crying out loud!
SOURCE: http://www.henrys.com/66366-NIKON-D3100-RED-W-18-55-VR.aspx

You'd be lucky to get 300$ for it if you included the 18-55… 150$ if it's just the body and even then… Why would I pay 300$ for something that is potentially out of warranty, potentially damaged (hidden) camera when I can pay just a bit more and have full warranty coverage and I know has not been mistreated.

The D800 is a rather amazing full frame camera, but costs $3, 000 without a lens.

Look instead at maybe a D7000 or wait until the replacement for the D300 is introduced. Both have APS-C sensors. Both are well within the range of your budget, but you will have to include the cost of a lens for them.

At best, you can get around 60% of what you paid for your fine D3100 and lenses, as low as 40% if you are in a hurry or there's any cosmetic damage to the camera.

Here is a link to all the lenses available for Nikon cameras

http://www.nikonusa.com/...index.page

You're already used to manual settings on the camera. Why upgrade? Why not just buy better lenses? I bet you can do exactly the same shot you can get with a D800 using your D3100.

Get a D7000 and some lens. If your not making your living of photography don't get a D800 or D(single digit) series. It would be a gigantic waste of money. Get a D7000 and a 24-70 or 70-200. Invest in glass more then y=into your body.