If you Google "wooden bicycle" or even "bamboo bicycle" (use "image search" also look at "fun bicycles" and "odd bicycles") there's plenty of crude whimsical examples...but I was pleasantly suprised and more impressed than I expected. A "trash day" MTB can provide head-tubes, BB's, drop-outs,...and a selection of bikes can even be bought for $20 at thrift stores.
If you can't afford a custom metal frame that accomodates a motor you want to use, or you wish you had an expensive recumbent...
Old chinese carpenter, Peijia Wu (crank rods ! no chain)
High school shop project, Marco Facciola
Close-up, wooden freewheel
Waldmeister, German work of art
Tandem work of art, Jens Eichler (plywood laminated, then shaped)
unknown Wooden MTB