I did a (metaphorical) jig when I saw this project ... turning an old guitar into a speaker seems like a very respectful re-use to me!
Guitar heads become wall hooks. Not a DIY ... but looks infinitely do-able to me!
One image from a great roundup of steampunked guitars
I recently posted a round-up of quirky, urban-garden planters that included a beautiful image of a guitar as part of a rooftop garden. I love the way this guitar planter frames the porch/veranda ... and still looks very much like what it is!
Newspaper, book pages and sheet music can quickly turn an old guitar into a piece of art or a clock!
This incredible piece incorporates an actual acoustic guitar - you have to see all the other images of this beautiful Guitar Table with compartments
Finally, recycle the strings by turning them into a centerpiece that you'll never need to throw out