I'm having trouble getting the bodies to display correctly with the heads. Like this screenshot here, where I'm using the Bewareofgirl Type 3 body mod.

http://newvegasnexus.com/imageshare/images/938964-1289396732.jpg

The neck doesn't match up with the body, how can this be fixed?

That's called the neck seam.

Not much can be done about it. Some mods have clothing items that cover it up,

Yep that's the neck seam it's been around since Oblivion as i recall. As Madcat221 said if it bothers you there's jewelry mods specially designed to cover the seam. I'm not sure if any have been converted over to FNV though.

point is that even the vanilla bodies have that seam in NV!!! and not a descnet one but one huge line... growlf is currently coneverting his oblivion body to NV tho and he should be able to make sure its gone, as far as i understood the textures simply dont match in vanilla nor the other bodymods

http://www.newvegasnexus.com/downloads/file.php?id=36661. Solves the problem.
Well, hides the problem

Dragon Age if you ever played it just included a neckpiece, choker, necklace, or something on every outfit. The base bodies have a necklace built in. Neck seams seem to be a common problem

I am using on of the chokers http://img574.imageshack.us/img574/2511/oddface.jpg. Kinda wish it was a small necklace or something.

I'm sure it's to do with the face generation software that quite a few of these games build into the game engine. The one Bethesda uses is a 3rd party program they added to the game engine to do detailed face generation. However i think the head is a seperate model from the body which is what creates the discoloration and weirdness.

We'll have to wait and see if they solved the problem for TES V. (you know they're making it)

Call it a gut feeling but I think it will still be there...

Even though I don't have neck seam issues with my male character, I http://img15.imageshack.us/img15/2882/74411424.jpg
I use Roberts for the body and can hardly notice colour mismatching anywhere. It's the female one I notice it most on.

Your archive Invalidation isn't working properly, for starters. See the seams down her side?
And then what everyone said about the neck seam - there will always be one.