From the Neck Up, An Illustrated Guide to Hat Making, by Denise Dreher. This is one of the "bibles" of hat making. While the emphasis is on the theater, it's chock full of basic and advanced techniques, all illustrated. Mine is dog-eared (can I say that without making the Steam Cat angry?). The book also includes a section on hat renovation, and a section of patterns for recreating historical hats. It's not easy to find, but you can get copies on Amazon or order directly from the author. The author also keeps an updated list of resources and supplies.

How to Make Hats, A Method of Self-Instruction, by Rosalind Weiss. Good news, this primer is available online for free. Click the link. It's hosted at the University of Wisconsin, where you'll find other hat books and periodicals, as well as books about sewing.

How to Make a Hat Base, from Threads Magazine. This includes a pattern for a non-blocked buckram fascinator base. Follow the tags for some other millinery tips.

Hatstruck Coture Millinery. Lee Duncan makes some very awesome hats, and also shares some of her knowledge. 

How to Make Hat Molds with Victor Osborne: This is from Threadbanger. Check out their You Tube Channel for some cool tutorials.

Vintage Fashion Explained: Kathleen O'Brien is an expert on vintage fashion, and has a book on smoking caps. I have that linked elsewhere here on the site. Her online collection includes several hats. Don't forget to check out pictures of her displays under the "Touring and Teaching" tab. There is also an extensive list of resources and references. (Disclosure: Kathleen is a friend who also provided the critters for the Infamous Three Ferrett Hat, which you can find in the Gallery.)

Historical Sewing: Jennifer Rosbrugh has tutorials and patterns. Great stuff here.

Vintage Fashion Guild Label Resource: Help in dating vintage hats and clothing, along with histories of various manufacturers.

Internet Archive: Publications on the subject of Millinery. Some items are in copyright and available to borrow, but most are out of copyright and available to download and use freely. One of my favorite items there is The Canadian Millinery Review from January, 1910. The magazine contains lots of pictures of big hats of the era, plus instructions on how to make some of them!

Judith M: A millinery supply company. They also offer workshops.

Hats by Leko: Another millinery supply company. And yes, they also offer workshops. Both stock a wide variety of products.

Hat Shapers: This site is primarily for felters, but you may be interested in their plastic blocks. They are also a source for Fosshape, a buckram alternative.

Adafruit Electronics: Looking to light up your hats, or just interested in wearables or other electronic supplies? Adafruit probably has it. (Psst. They're also one of the top woman-owned companies in the US.)