For large areas I use a disk like these on an angle grinder. The ones I use come from The Home Depot.
http://www.amazon.com/3M-SandBlaster.../dp/B000BQURDI
They don't do as well on small parts, in corners and other hard to get into areas, but they do move A LOT of paint in a hurry.
If you use these (or a similar product) on the larger areas and a wire brush on an angle grinder for harder to get to areas, it really does cut down on the time involved.