I've had any number of people ask where they can find a certain fake fur fabric, or just where to find good fabric in general. Now here's the list of the websites I regularly order fabric from, with my own views on where to go for what!

Premium Furs
I list this one first because, although I can't afford to get fur there very often, and they don't actually have the best selection, their furs are amazingly high quality and I love them, especially their shag fur. The Treehouse squirrel was made from it, and it went into my Ziazan Kitsune costume too. Feels exactly like real, soft cat fur. I've worked some with their Tissavel animal fabrics as well, and they are stunningly soft. If you have a few bucks to blow, I highly suggest getting their complete assortment of sample cards, just so you can pet the fur and drool. You probably won't be able to afford to buy any of the animal furs, but you can always dream, right?

CR's Crafts
Here's where I order the most often. They have a huge selection, and most if it is wonderful quality. They carry the Montery Mills fur, which is my second fav. shag, and I use it a lot. But beware! The MM shag is listed under "fox." Don't touch the other shag fur they carry, the "fun fur," it's moderately horrible stuff. I have used it for some things, it's not totally worthless, but the texture and look and durability of it are all pretty bad. The only thing, other than the shag, that's not good about them is that you have to pay for sample cards.

Distinctive Fabric
I order from them nearly as much as from Crs, and their long shag fur is almost as nice as the stuff from Premium. The selection here varies, and a lot of their colors are special order only, so you have to buy multiple yards of something, but I find it worth it because their prices are great, their customer service is wonderful, and their selection is excellent. Just be aware, when ordering the long shag, that it comes in two types, the "original" full type and a "stringy" type. For a fursuit you probably want a full type, the stringy fur tends to clump up and wants to lie flat rather than looking fluffy.

I'm Stuffed Fur
I've bought fur here a time or two, but I should warn you, though they've put in an online ordering system, I've had no luck at all using it. The gal who runs this place doesn't seem to be very comfortable with e-mail, and she screwed up my order, which has never happened when I've phoned it in, so I strongly suggest you do all your business with them by phone, and NOT through the internet. I've found it can definitely be worth the bother of a call, just because the gal who runs it is so very helpful. They have eeeeeeeeeeeeeverything, and I mean everything. Their Coyote furs and animal prints are wonderful! And they send free samples. It'd be a complete rave review, except they're a touch overpriced. Not bad though, and sometimes it's worth it to get just exactly the perfect fur.

Denver Fabrics
These guys have some very nice furs, at very good prices. What they have in stock varies a lot though, so if you see something there that you like, order it when you see it, it may not be there when you come back! They do have swatches, though you have to pay for them, but as the quality of their fur can vary wildly, I'd suggest getting a swatch first. But order asap after your swatch comes.

Faux Paw Furs
I've bought from them exactly once. Their customer service was good, but they're pretty overpriced. Still, the fur I got was top-notch quality.

Carol's Zoo
Another place I've bought from once. They're also a touch on the expensive side, they seem to cater more to high end plush makers than to costume or fashion use, so their stuff is priced for small quantities. But I got some tabby pattern short fur there that I am very pleased with.

MJ Trends
I get snakeskin, pleather, and other leathery or scaly or variously non-furry fabrics here. This was my source for the shiny fabric used on the dolphin tail, and I got some very spiffy pink pleather for a rat tail here as well. Good service, decent prices.

Montery Mills
Wholesale by the 15 yard roll only. You can get all of their furs through CRs, but they're a ton cheaper direct, if you can just find a use for 15 yards of fur! I quite regularly order black and white fox this way, both are colors I use a lot of.

People I haven't actually ordered from:

Make Me!
Sy Fabrics
Plushfurs.com
Mendel's
Big 4
Calico Pie (In the UK.)