I am a consumate pack rat. I collect all sorts of things (hats, hair flowers, shoes, Norwegian troll sculptures, tiki mugs, etc), and while the hoarding of items is usually attributed to material goods, I tend to do the same with web links. Often I'll see clothing items that I can't afford at the moment, only to curse myself later when I check back and the item is gone. Sometimes it pays off and something will go on sale and I'll jump up and down with pride for my patience.
All this rambling actually doesn't at all have to do with clothing per se, but a link I found ages and ages ago and have constantly kept bookmarked in my files. It is on wikihow (I guess wikipedia's how to guide?) and is called "How to Dress in the American 1940's Fashion". Aside from all the wonderful instructions and references, it gives additional tips for creating your own vintage look, as well as links to other 40s fashion sites.
Some highlights from the article:
Fashion from the 1940s is such a classic look that it never really goes out of style. You'll find that almost anywhere you go wearing 1940s fashions, you will get a lot of positive attention. This article explains the look of the times and aims to help you convert clothing from current times to carry a more 1940s flair, as well as giving some key tips on hairstyles, accessories, shoes and other relevant items.
-Consider the fabrics. Get tweeds, wools, silk, linen, cotton, or blends of these. Keep in mind that some synthetic materials, such as nylon and rayon, had already been invented. Rayon was quite popular in women's fashions, as a substitute for silk, which the military was using for parachutes. All the same, many fabrics we have now were not in existence then but you may be able to get away with it.
-Small hats were popular, also with netting that would hang over the face. A high-fashion woman may have worn large hats. These would often have little or no brim in the back and a high oval rim in front, which may have been any angle above the face. A woman's hat similar to a fedora began to be popular.
-Lipstick was still darker shades of red, maroon was popular. Mauves and corals were also popular, and Tangee lipstick, the original color-change lipstick, is still available. It was still common to fill in lipstick beyond the lip line, especially to emphasize the curve of the “Cupid's bow” of the top lip to more of a gentle arc.
You can read the full article here
or if you're looking for more great reference material for the times, this book is fantastic:
For sale via amazon.com for as little as $7.09!
Since it's clothing that was for sale during the time, not just what the upper class and movie stars wore, it has great illustrations for helping to put together an authentic look of your own.