What works better than the environmental angle is reminding them that you are saving them disposal fees. My last four big jobs were from "clean-out" companies. The last one was a bunch of monitors and electronic stuff from a company upgrading their equipment. They hired a guy to dispose of the old equipment. He, in turn, put an ad on CL for "a few monitors" under the "FREE" section. I responded and got a truck and trailer load. So, use CL, contact them in person, send flyers or anything else to let them know you're out there. If you contact someone who can't help -- Oh, well.