The Tesla Valve: One Way Flow With No Moving Parts
The whole field of fluidics is fascinating, including entire digital logic families that operate at kHz rates with no moving parts and no electricity, just air.  I wrote a kragen-tol post about this in 2002 http://lists.canonical.org/pipermail/kragen-tol/2002-April/0..., when Air Logic still sold actual logic gates that ran on air, but since then Google Books has archived this June 1967 Popular Mechanics article, "How They've Taught a Stream of Air to Think": http://books.google.com.ar/books?id=jSEDAAAAMBAJ&pg=PA11..., and of course fluidics has become practically very important for on-chip microarrays.  There's also a Wikipedia article now: http://en.wikipedia.org/wiki/Fluidics