Help need Protrait Lens for D3100

In case you do want a prime . . . .

For a real portrait lens, a good 60mm is an option. The Nikon 60mm 2.8 is an excellent, fast-focusing lens. It has a 35mm equivalent of about 90mm, which is really good for portraits.

After looking at that lens I bought the Tamron 60mm 2.0. It does not focus as fast, but is brighter and has been a pleasure to work with for the past year or so. Also has an equivalent length of 90mm.

Both lenses will do 1:1 macro as well. I actually find I am using the Tammy more for that than portraits. A second benefit of the Tamron is that it is usually offered with a substantial rebate. Both lenses are motorized and will work on the 3100. They are not VR and stabilization is really not much offered in the 50-60mm prime range.