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 .  

Currently there are about 10 known asteroids having a period of about 1 year .  
Only two of them 2004 GU9 and 2006 FV35 seem to be locked in resonance around  Earth.  
Others , as Cruitne are in a horseorbit around Earth .  
Hereunder is an animation of 2004 GU9 and 2006 FV35 covering 200 years from now in rotating frame to Earth .