I just picked up a copy of Jane Gordon's Technique for Beauty (no printed date, but clearly from the early 40s as chapter 23 is all about looking good on war rations).
Some bits of this book feels surprisingly modern in tone. There's a lot of emphasis on good nutrition, proper digestion and the like. I haven't had a chance to read through it in it's entirety, but a thorough reading of the first chapter, and a quick peruse of the rest has not revealed anything glaringly dangerous (like you often get in older beauty manuals).
This modern tone also makes it ever so slightly disappointing, because all the emphasis is on maintaining the quality of the hair and skin and there isn't really anything in the way of makeup colour palettes or pin-curl sets. It that respect it's not very useful for those of us looking to recreate authentic period looks.
There's not too much in the way of illustrations in this book, but the ones that are here are quite charming and I thought I'd share a few below. (Please excuse my rather low budget photos here - I'm making do with an old "point and shoot" and the editing capabilities of iPhoto)