In the Near Earth Objects database
http://neo.jpl.nasa.gov/cgi-bin/neo_elem I've selected two large asteroids having a period of 1.50 years , hoping they show a resonating behaviour .
In this animation (in rotating frame on Earth )over about 400 years 2005 GP21 (in red )and 2000 LY27 (in green) indeed show a librating resonance to Earth .
It may look as if both asteroids once have the same orbit . This isn't the case . In fact they are in counter phase .