PorterhouseMusic
Mitakuye Oyasin
Les Claypool of Primus used to play one. Scroll to the 4th one down.I've heard about semi-fretless guitars. Never seen or hard one in the flesh though.
Edit: actually - that's just a fretless bass. Maybe I was just mistaken about that.
Les Claypool - Carl Thompson - Fine Handmade Instruments
Carl Thompson has been building custom order, hand crafted and completely unique basses and guitars since 1974, including the first electric 6-string bass and piccolo bass.
ctbasses.com