In reply to Rog Wilko:
Yep the Conti Gatorskins are particularly difficult. You almost have to stretch them in phases with new ones. Failing that get a Crank Brothers Speedier Lever tyre lever, I use one of these at work (in a bike shop) and they are by far the easiest way to get tyres on and off, with practice you just need to use the one lever.
You could stick a bit of washing up liquid around the last section which might help.
Yes folding tyres will always be easier to get on/off, but each has their pros and cons.