I've built one mandolin and part of a dulcimer. I'm not happy with either. Hopefully, I'll be doing other such things in the future.
Here are some interesting links.
General and Vendor Links
Kathy Matsushita, Amateur Luthier Genius
Elderly Music -- where I bought my lute
Associated Tool and Instrument Technique Links
Instrument Building Instruction
Makers and Other Associations
Instrument Kit Links
Flutes and Flute-Like Instruments