One web site that I visit frequently (will be there in a few minutes) is Hillsdiscountflies out of Yakima, Washington. Been buying from them for years without a bother.
But, one of the great things about the site is the hundreds of colour photos of fly patterns. It's a trip just to page through and (as will be the case shortly) drop a few bucks.
Tie most of my own, but when I get down to size 10's and below ......... at 68, I'm not the Guy I used to be.