What Standard Lens Is Best?

I have a Nikon D3100 and I was interested in getting a standard lens that I would be able to use for face portraits, torso/face portraits, and full body portraits. I want to be able to do all these different perspectives with a particular lens without having to go back from the subject very far. The lens I would like would definitely have to be able to manual and auto-focus and would hopefully be able to be used still if I upgrade to a D90. I was looking at these lenses and was curious what your suggestions would be:

http://www.henrys.com/24040-NIKON-DX-NIKKOR-AF-S-35MM-F1-8-LENS.aspx

http://www.henrys.com/857-NIKON-AF-S-50MM-F1-4-G-LENS.aspx

http://www.henrys.com/65185-NIKON-AF-S-50MM-F1-8-G-LENS.aspx ***

http://www.henrys.com/26232-SIGMA-30MM-F1-4-EX-DC-NIKON-HSM.aspx ***

http://www.henrys.com/719-SIGMA-50MM-F1-4-EX-DG-HSM-NIKON.aspx ***

The ones with stars beside them were suggested by different people at Henry's at two different locations and over e-mail!

I don't know which one would be best!

Going from your 3100 to a D90 is not much of an upgrade since the 90 is a 2008 model. Going from a newer camera to an older camera is a waste of money, even though the 90 has a couple of features your 3100 doesn't have. All of the lenses you listed will autofocus with your 3100. Out of all of the ones you listed, I would recommend the Nikon 50 1.4 AF-S - if your budget is lower, get the 50 1.8 AF-S. The Sigma 50 is a great lens, but very expensive.

For portraits the 50mm is best. A slightly longer focal length lens is better so the face on portraits doesn't look longer with exaggerated noses etc. The f1.4 aperture i feel is unnecessary and would demand a much higher price for very little discernible benefit.

I have used 80mm f2.8 with my old film cameras (the approximate equivalent of the 50mm with the d3100) and you can get nice blurred backgrounds even at f2.8 so f1.8 is only better. The 30mm will be like standard lenses and are too short for portraits.

I'm not sure which Auto-focusing lenses the D90 uses but I think it is different to the d3100. Compatibility may be an issue.

If you stick with the D3100, you will want to buy the Nikkor AF-S 50 mm if you wish to shoot portraits.

If you want a single lens solution, then the Nikkor AF-S 18-200 mm could be the one, but you will have to save your pennies for a while longer.

As far at the D90 is concerned, it will allow you to purchase the legacy Nikkor AF lenses, which usually costs less than the newer AF-S lenses.

If you have had the D3100 long enough, you should know what lens you really need.

I'm sure that if you tape your 18-55 mm lens to 50 mm and shoot at that focal length for a week and then tape it to 35 mm and do the same thing, you will be able to figure out which is the best for you

The 35mm 1.8, 50mm 1.8 and 50mm 1.4 are all pretty good. For portraits I prefer the 50mm ones.
The 50mm f/1.4 is a bit faster and probably the best out of those, but you'll get great results with the f/1.8 as well.
All of the lenses you've listed will work with both the D3100 and the D90. As Taylor said, it might not be the best idea to upgrade to a D90, since it's an old camera. I'd suggest a D7000 instead (if it's in your budget).

Whichever lens, remember your camera has a focal length multiplier of 1.5x (also known as crop factor). For example, a 50mm interchangeable lens with a 1.5 multiplier would have an effective focal length of 75mm:

50 X 1.5 = 75

A prime lens often provides the best quality, however a zoom lens is more versatile, such as one with a focal length of 17-50mm and an aperture of about f2.8, which allows you to shoot at lower ISO numbers in low light. A lens with f1.4 or f1.8 is even better.

A 50mm is not a standard lens on that camera, it is a short tele lens, a portrait lens. 30mm or 28mm is 'standard' for the DX-sized sensor in the D3100 and D90 and D7000. If you are photographing wide scenes from a close distance you will need a wide lens, maybe 22mm or 18mm.
If you already have a 18 to 55mm with your D3100 you will be able to see what a range of focal lengths will do for you - a 50mm will be close to your lens at 55mm.