Really useful sites
The RPF (Replica Prop Forum) is a wonderful message board full of amazing people who are devoted to getting every detail right. If you're looking to get a t-shirt from Scott Pilgrim or make your own Iron Man armor or anything in between, this is the place for you!
This is the home of the Stargate Fandom. Well, that's how they put it. It's the Stargate equivalent of the 501st. You don't have to be a part of the group to benefit from the information they have on the site, though. They have wonderful, detailed lists of what you need to create your own accurate Stargate uniform. I used them for my own SG-13 Woodland uniform.
The Starfleet 1701st
"This is the club that dares to be the answer to a Star Trek fan's dream: to possess an accurately made uniform and join others for fun times in that uniform!" This is the Star Trek equivalent of the 501st. It is a wonderful community full of great information on how to either make or buy your own accurate Starfleet uniform. This site is where I found out about the wonderful Anovos.com (see below).
This is the place you need to start if you're even remotely interested in doing any type of kimono. This breaks down the kimono and the hakama into easy to understand terms and makes it seem much less overwhelming. He also mentions little things that so many leave out, like sleeve length and where to leave things open. So wonderful!
Anne Liese's Fibers and Stuff
This is the best guide for kimono widths that I've seen so far. But I haven't done a ton of looking since finding out more. Just pay attention to the measurements at the top of the page for the hitoe and then follow the information from Valkoinen Samurai.
Craft Foam Armor
This is a great tutorial on how to make armor out of craft foam. Really this can be used for anything you need to make from craft foam. Really good descriptions and easy to get materials.
This is the place I go to if I need a wig. They have a rainbow of colors in a wide variety of amazing styles in heat resistant fibers. And they are really affordable for some great quality wigs!
Jo-Ann Fabric and Craft
This is my first stop when it comes to craft stores. They always have great sales going, and they have wonderful coupons that you can have mailed, e-mailed, and/or get on your smart phone. They make it quite affordable to get a lot of supplies.
This has become my back-up to Jo-Ann's. Their prices are usually similar, and their selection is better or worse depending on what you're looking for. They only have one coupon per week, but they do accept competitor's coupons.
This site has some of the best compression tops out there for Female to Male crossplayers. Their Tri-Top is constantly recommended for FtMs because it is strong yet it allows you to breathe.
These guys are great! They have a very wide variety of socks, tights, arm warmers, gloves, leg warmers, and so much other sock related stuff. If you need socks for your cosplay that aren't the simplest thing, check here first. They're really affordable, use wonderful fibers, and even have eco-friendly socks! It's amazing!
Need glasses for a cosplay? Look no further! Cheap, great quality glasses of all shapes, sizes, and materials are here. It's a great resource for glasses.
This is an amazing place to get patches and pins for your uniforms. It's also a fun place to go geek shopping.
From their site:
ANOVOS represents the pinnacle of quality in screen accurate uniforms and prop replicas accomplished by the manufacturing and marketing of limited offerings from movies, television and contemporary media.