A lot of people use http://www.fallout3nexus.com/downloads/file.php?id=6341. I've used Anthony Ling's Pretty Things (can't link because of some of the pics) and like it with the exception of the outfit it dresses Moira in. Those are really the only two major NPC overhauls I know of. The others like Pretty Girls only affect a few people.
That outfit that Moira had on with Ling's just drove me nuts - every time I saw her I just wanted to scream at her, "Put some [censored] clothes on, woman!"
One of the first things I did once I figured out the basics with the Groovatron was to give her a decent outfit.
There's a couple of other gripes I have with Ling's Pretty Things. It completely made over Tiffany Cheng at Tenpenny into a hot young Asian girl. Not that I mind hot young Asian girls (
), but when you talk to them and they reply in an old woman's voice, it's a bit ... jarring. Overall I like the mod, though, and I still use it.