Well hell if you all are going to mention all those stores I might as well say that I get all my yarn supplies from Knit Purl. They have a huge selection of Koigu, kits and exotic fibers (silk wrapped stainless steel) from Habu, the Shibui line of patterns and yarns, and much more. Flat rate shipping of $6.50.
Most of these have already been mentioned, but these are just a few that I have ordered from recently:
p.s. If anyone is looking for a free pattern. check out my Column of Leaves scarf and matching hat. 
I want you to know that I have printed out your scarf pattern and it is on my to-do list once I find the right yarn for it. ( The Stash I have is just not good enough. It isn’t worthy of a Doper Created Pattern, dontchaknow.) D’ya think it would knit up well in Kraemer Vintage Alpaca
And I now have yet another yarn site stored in my favorite places. It’s a lovely site, major yarn porn!
I also have another site to recommend, which I don’t think was mentioned yet - Kaleidescope Yarns. They have a large selction in a lot of price/fiber ranges. I’ve ordered from them several times, and have always had good service. When I’ve e-mailed them to ask questions on an order, they’ve always responded the same day.
Yes that would be perfect! I think any solid color, aran or DK weight wool, alpaca, or blend of the aforementioned with cashmere or silk would be the best! I think the design really looks the best in a solid, light color. I made it with a darker multicolor, but after seeing ones that other knitters make, I really think it looks best in a light solid! The leaves pattern really “pops.”
By the way, I have to mention this pattern is really easy and fast. That is the best part about it. Oh, and the most important thing about the pattern is you must block it when you’re done. It’s crucial to define the pattern and stitches, and to open up the YO holes.