How to Make Yourself a Dressform
(I recommend the brown paper tape version; it is easy and really cheap, and it has history behind it--the technique goes back to at least the 1930s.)
Online directions for making an A-line Skirt without a pattern
Covering Our Hair
Links to directions for making headcoverings. (Some are knitted or crocheted, instead of sewn.)
Dawn's Costume Guide
(mostly SCA, but there's a section on Biblical-era costumes, such as children might wear at church plays) Tells how to draw out patterns based on your own measurements; some of the patterns could be adapted slightly to make contemporary garments.
The Tangled Web
Another SCA or RenFaire site. Directions include how to make a chemise (which could be adapted to make a peasant blouse or a nightgown), a gathered skirt, a gored skirt, and bloomers.
The Beginners section has free instructions for making several period garments for the upper body. Use your own measurements to make your pattern pieces, then use one of the fabric-saving, probable period layouts to cut your pieces. (Outside the beginner's section, there's a lot of interesting historical information, plus a few how-tos; read to learn what your northern European or Japanese ancestors were wore.)
The above three SCA links are links I am familiar with. Here's a big collection of links to pages with SCA clothing information--at least some have construction how-tos.
Bills itself as "the most complete online stitch reference". Has illustrations and videos to help you learn crochet, knitting, embroidery, tatting, etc. (Okay, so knitting and crochet aren't sewing, but embroidery sorta-kinda is and the videos are a cool resource.)
About.com can be annoying, but their Sewing section has a Free Projects subcategory
has an online library of articles covering multiple sewing-related areas.
Threads magazine (the source of the dressform how-to above) has a collection of articles online.