Dwarf mistletoe, a parasite on various pine trees, use hydrostatic pressure to expel seeds at speeds up to 60 mph. (Years ago I worked on computer models of forest growth, health, and diseases—one of which is mistletoe.)

http://www.apsnet.org/edcenter/intropp/lessons/miscellaneous...

Reminds me of my favorite title for a scientific (engineering) paper ever:

Shooting Mechanisms in Nature: A Systematic Review

http://journals.plos.org/plosone/article?id=10.1371/journal....

(disclosure: I work in the same department as the authors, although not at all involved in this work)

Somewhat common in the eastern US is Wisteria, which also has an exploding seed pod.