I have to add my support for the Martin 15 series. We recently fell in love with (and just had to acquire) a D15 which is a Dreadnought with solid mahogany top, back and sides. For a new uitar this thing has a stunningly "big" sound with a deep hearty mid-bass and bell-like upper register. The neck is a dream to play and if your fingers get too sore to play it - you can just smell it --mmmmmmmmmhhhhhhh!

Very reasonable price too.

Cheers
Jon