I have about a 400 dollar budget for some lenses - here is what I have found lined up and the prices I have found- what would you go for with 400$ to spend on lenses:
Sigma 18-250 - 320$
Nikon 18-105 - 175$
Sigma 18-200 DC (No OS) - 175$
Sigma 17-70 (No OS) - 254$
Sigma 18-200 DC OS - 275$
Tamron 18-200 - 139$
None of the above.
I'm actually quite surprised at the popularity of the 18-105mm f/3.5-5.6G VR here. I have one only because I didn't want to wait for the D7000 body-only kits to become available. Can't wait to unload it on Ebay.
You may have different goals, but as I've said before, I personally don't see any value in an f/5.6, 105mm lens, simply because its maximum aperture is too small to isolate your subjects from their background. A larger-aperture lens will allow you to do that by employing shallower depth-of-field. And, since 105mm is an excellent portrait length, you're likely going to want to do that more often than not. A head-and-shoulders portrait, shot at f/5.6, at 105mm, will tend to have too many distracting background elements still in-focus (unless your background is very far from your subject).
I know you already sold your 18-55mm f/3.5-5.6G VR lens, but I would've kept it. It's sharp, small, and it has VR, which nearly makes up for its slow aperture. I basically use my 18-55mm VR as an 18mm wide-angle "prime," with the added bonus of VR.
What would you do?
If I had only $400, here's the glass I would buy for a DX body:
1. AF-S Nikkor 18-55mm f/3.5-5.6G VR; $99, refurbished (used primarily as a 28mm-equivalent, wide-angle "prime").
2. AF-S Nikkor 35mm f/1.8G; $190 (50mm-equivalent, "normal" lens).
3. AF Nikkor 50mm f/1.8D; $130 (75mm-equivalent, short-telephoto for portraits).
This is simply the modern, DX-version of the classic three-lens, beginner's set-up, back when we all used to shoot with "full-frame," 35mm film SLRs: a 28mm, 50mm, and an 85mm. In fact, those were the exact three lenses I first bought when I got my very first 35mm SLR (Canon). When I switched to Nikon, I changed to: 24mm, 35mm, 50mm, 85mm.
If I had a bit more to spend, I might replace the 50mm with either the f/1.4 version, or get the AF 85mm f/1.8D instead, for portraits. Later, as Tao mentioned, if you want to get some reach, you could add the 70-300mm, which is also pretty inexpensive. Also, an excellent way to greatly reduce lens-changes, is to carry two bodies (sorry, but I would've kept the D40 also). You may not think these lens choices are "right" for you, but that's what I would do.