I really like MT's mosquito/fly pants idea.  [smiley=thumbup.gif]
I would like to add that Avon's Skin-so-soft does work somewhat on the ankle biters, deters them longer than sun screen.  It can be diluted some with baby oil and then isn't so strong smelling.  Deet works for a while to keep them at bay.  
Lately I've been taking a light weight mosquito screen tent on our trips when bugs may be especially bad.  Then we have a place to retreat to, besides the sleeping tent, if the ankle biters are especially bad.
We use the ankle biters as a barometer...they bite like crazy just before it is going to rain.  I think moving to a different site often helps leave the flies behind...they seem to be worse on some (probably dirty) campsites than others.  We also always take fly swatters along in fly season, it helps in the canoe when you have only a few.  It is less helpful in camp where there might be lots of flies.
I use the wait and swat method for horse flies.  They are slow to take off and easy to hit.  With deer flies you can hold both hands up over your head (as tho appealing to God)...99% of the time they will land on your hands (thinking they are ears ??) and are then easy to grab or slap.
Ankle biter flies almost always take off going straight up from where they are perched...it is effective to place your hands about 10 inches above the fly, hands about a foot apart, and clap them together above the fly as it takes off.  The fly will often end up between your hands and you will be successful at killing it.