Beaverslide Dry Goods - ranch-raised, family-run, mulespun yarn
Colonial Yarn Shop - My local yarn shop but you can shop online and enjoy the goodness
Etsy - lots of indie-yarn dyers. Have fun searching this site.
Knitspot - Anne Hanson has incredible patterns for the knitter here.
Little Knits - Always some bargains to be found at this online vendor's website
Loopy Ewe - My favorite online yarn & supplies vendor, hands-down.
Ravelry - an online community of knitters, spinners, and weavers. This site has invaluable resources for anyone who enjoys working with fiber in any form.
Spinning Loft - Beth is a great online vendor for spinners (and she's a wonderful instructor with an actual store in Michigan, if you're up for a road-trip)
Spunky Eclectic - More spinning and weaving supplies
Twisted Fiber Art - Unbelievably gorgeous yarn colorways here