At long last, I added some new free downloadable instruments in the app. Go to Sound->Download Samples to grab them!
Violin Staccato - pulled from the archives, a companion to the built-in Violin, recorded in the same session by Steve Bingham.
Shakuhachi - a Japanese flute
Turkish Ney - a rim-blown flute made of reed
Snake Charmer - reeded wind instrument. Add your own expression with shake/tilt.
Plus two more from Michael Eskin (http://tradlessons.com):
Hohner AirBoard - the new melodica from Hohner
Cajun Accordion - sampled from a Hohner Cajun IV one-row accordion
Bonus: the Harp instrument is updated, the background hiss is now gone! Re-download it...
And coming very soon -- once ThumbJam v2.4 is approved -- several new velocity-layered instruments will be released, to take advantage of the new feature.