The original use of L-systems is to model the fractal-like forms that appear in plant growth. Johan Knutzen gives a nice overview with pictures in <A HREF="http://www.cse.chalmers.se/~uffe/xjobb/climbingplants.pdf">Generating Climbing Plants Using L-Systems</A>.

More recent applications include musical compositions with a self-similar structure, as described by Stellios Manousakis in <A HREF="http://www.sonology.org/NL/thesis-pdf/Stelios%20Manousakis-Musical%20L-systems.pdf">Musical L-systems.</A> (This musical rendering of L-sytems has been called <A HREF="http://www-users.cs.york.ac.uk/susan/bib/ss/nonstd/eurogp05.pdf">Growing Music.</A>)