We did some analysis on this and actually found that Pine (i.e. soft white-wood) had quite a decent ring to it. However, as you'd probably expect, it dents quite easily.
Have a look at: http://rufusguitars.co.uk/info_woodtypes.php
Almost everyone we are making guitars for at the moment (worldwide) has chosen Cherry for their guitar. Our tests show cherry, like pearwood, to be very sonorous and resonant; I often wonder if this is because it comes from a small tree with plenty of grain variation. Also cherry and pear, being top-fruit, are closely related (i.e. Amygdaloideae, in the Rose family)
I really can't comment on plywood except to say that this website says that all the major brands make their semi's from it: http://www.edroman.com/guitars/rvc/bluesdeluxe.htm
However, in the major brands defence, I would expect that these companies would prefer to use the word "laminate"!
Most hifi speaker cabinets are constructed from chipboard and I was always told that this was to absorb the sound - if that's true then it wouldn't be a great material for a guitar.