Most double bass pickups are based on piezos as well as the pickup in my ashborys. Also of course acoustic bass guitars and things like godin & rob allen basses which look acoustic, but are more like solid bodies.
I made a cheap & cheerful banjo pickup for Pete, o5b's guitarist using a lid from a colman's mustard jar, a cheapo piezo disk element from Maplins, double sided car-trim tape, a chunk of mousemat, a few inches of mic cable and an inline 1/4" jack. It also Sounded Pretty good mounted on my precision when I tried it out at home.
Here a live recording of it on it's first tryout - click the MP3 thingy: [url="http://www.o5b.co.uk/petes-banjo/"]http://www.o5b.co.uk/petes-banjo/[/url]
I was pretty chuffed that it sounded OK and didn't feedback - I don't think we even used a preamp - it went straight into the guitar amp if I recall correctly.