The ones you find in stores are often commercially tied by Matt Bennett (aka Fly Geek) but he doesn't seem to have them on his website at the moment.
Matt Bennett is the man! His flies are the best patterns for the clear waters of Central Texas and even though they cost a bit more, he ties on solid hooks with premium materials and keeps durability in mind. If you see something on
on his website that's not listed online like the llanolope, saltwater flies, or hill country clouser, just shoot him an e-mail. He will spin them up for you (although it may take a bit of time).
A big reason I started tying flies was to be able to get patterns that aren't readily available everywhere else (mostly carp flies). It's really not too difficult once you get the basics, especially since there are some
great tutorials that walk you through the steps.
There are lots of great flies already mentioned on this thread. The only thing I will add is that I usually size up my bluegill flies. Since they are so aggressive in the waters I fish, using a little larger fly keeps them from inhaling them and prevents having to perform minor surgery while unhooking and releasing fish.