I have been using what ever the local hardware store has for epoxy when coating my flies, but it is very thick, and I sometimes have trouble getting it smooth especialy where I try to taper it off onto some kind of fiber. What have people found to be the best brand, and/or can I just thin it down a bit with some laquer thinner.
I use regular 5 minute epoxy. What are you applying your epoxy with? When I want a light finish, I use cheap arts and craft brushes and put on a little. And, sometimes I apply a couple of light applications of epoxy - easier to control.
I use clear 5 minute Devcon (hardener and resin) and have had no problems with it. I use toothpicks (small flies) or the small cheap throw-away plastic paint brushes for applying it (batch by batch) on the flies when they are turning on the rotary motor (depends on the size of the fly which one I use to apply). Otherwise for just coating flies, I use a cheap throw-away plastic paint brush. If there is a better way to apply it, I’d like to hear it also. 
Depending on the number of flys your considering doing Flex-coat epoxy rod finish is very easy to work with as are most rod finish epoxys. You will how ever need a low RPM motor and cureing wheel. For example I do many hunders of epoxy flys each year and have learned a lot of simple tricks to make working with it much easier. work with epoxy is more about technique than tools. If you have or have access to a drying motor let me know and perhaps I can help.
For flies where I just need a thin coating on a head rather something for bulk and structure, I have been using Loon Hard Head. It is thinner than epoxy and does not need to be mixed. Multiple coats can be used of some build up is necessary. It comes with a brush on applicator. It still helps to have fly turner of some sort. I use it for things like heads on Alfs or Flashy Profile Flies, Sea Habit Bucktails and similar patterns, heads on decievers and clouser minnows, coatings for foam or cork poppers, just to name a few of my applications.