Double white dwarfs
AM CVn stars
Black hole binaries
LISA wiki (verification
Physics Today article: Ultracompact binary stars
I wrote an article for Physics Today, which appeared in the July 2006 issue, page 26, and may be found here.
For personal use I can provide an offprint (just let me know and I'll send you one, I have plenty) or a PDF file of the article with the following disclaimer:
Copyright (2006) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.