Knit Picks! I used to be so in love with this place it was almost frightening! But now, I have come to realize that most of their yarn has pretty low yardage. Sure the prices look good, but you are also getting about half the yarn, so, it's not such a great deal! And the 'free' shipping amount has gone thru the roof! They used to put coupon codes in knitting magazines for discounted or free shipping, but I have yet to see one of those in a long time!
If you want some great deals on yarn, try Little Knits! Sure you have to buy $25 worth of stuff, but it's so easy with all the sales she's got going on!
Of course you can go to Discount Yarn Sale too, that site always has great prices & a huge selection!
WEBS is good, and it's site has lots of stuff & has discounts on larger orders.