Part 3 - Graphical Mods

Bodies & Heads

Better Bodies by Psychodog Studios

Replaces the original segmented body models with smoother, continuous ones.
Lore-Friendly Better Bodies Underwear by Yar-Yulme

Vanilla-friendly underwear textures for Better Bodies.
Westly's Pluginless Head and Hair Replacer by Westly

Replaces all the heads with more detailed ones that are close to vanilla.

A notable alternative is Better Heads (formerly known as Faces of Vvardenfell) by Gorg, Arathrax (a.k.a. DarkSharp) and Motoki, but it is much less vanilla-friendly.
New Beast Bodies by LizTail

Better Bodies equivalent for beast races.
Pluginless Khajiit Head Pack by ashiraniir

Replaces the 8 Khajiit heads with more detailed versions.