The conference call with Bill Bottke (MP3 plus other documents) about "minimoons" presents an alternative to Asteroid Redirect first got me interested in orbital mechanics. The idea is that there are enough small asteroids that approach the earth-moon barycenter (EMB) that it seems likely there are frequent temporary captures of small asteroids into chaotic 3-body orbits in EMB system, that last for a few months to a few years.
Here is an example of one theoretical orbit from here or here:
One can read more in Granvik, Vaubaillon and Jedicke 2012 (The population of natural Earth satellites Icarus, 218 (1) March 2012, pp262-277) available without paywall in ArXiv.
Only one "minimoon" 2006 RH120 was known by 2012, but it seems there should be new ones regularly, according to Granvik et al. 2012.
Have there been others that were detected and reported?