Hallgarth's Additional (Vanilla) Hair by Hallgarth
Mod does exactly what it says; adds a number of new hairstyles and beards to the game that fit perfectly within the vanilla style, giving a much greater degree of choice to just about every race/sex combination. Just downloaded the other day, checked it out in game and I can't see it ever leaving my load order. Works with hair retextures (SLFH). I've been looking for something like this for quite some time, and I personally feel like it's a prime candidate for STEP - certainly for Extended, but with how seamless they are with vanilla hair I'd say Core. Not that I have any dog in that race.
There are a couple issues with some of the meshes, but there are still a couple vanilla hairs with mesh issues, so not a detractor for me.
As a sidenote a fan of the mod has applied it to NPC's;
Hallgarth's Hair for NPC's by IndigoCrow
* a couple issues here, however; primarily that the author hasn't carried forward USLEEP fixes. For some reason also flags a couple vampires with 'prey faction'...