I recently replaced a hardwood floor and it took two guys an entire day to do the demo work. The work would have gone faster if they had used a Hardwood Hog, a pneumatic tool designed to pry up flooring. After connecting the machine to a portable compressor, the operator jams its teeth into the groove or under the tongue of the flooring, hits the trigger, and a pneumatic piston raises it up.
The Hardwood Hog is an offshoot of The Shingle Hog – a similar device for stripping off asphalt shingles. Neither tool is cheap (the flooring model sells for about $1900) but according to their maker, they'll pay for themselves by reducing labor and time lost to injuries.
I can't vouch for this tool because I haven't used it or seen it in person, but it does look interesting.