Our townhouse just had 2 wasps hives that we had to get rid of. The best way to rid of wasps without using a harmful chemical is through smoke. But it will not make the wasps go away. Finally we had to call the pest control who said that once the nest is built there isn't any safe method to dispose of it. So, in short, it is a bit of a hippie pipe dream. I did find out that if you can capture the Queen, then you dont have to get rid of the nest. The workers will simply go away, leaving you with an empty nest. And the Orcan guy said that's happened a few times, they got lucky and captured the Queen hornet. But, I do know of a safe, effective and harmless way to never get a wasp hive again, once you've gotten rid of it. And it is safe, non toxic and doesnt use insecticides. Wasps are territorial creatures, so they will not build a hive next to an existing hive. There is a company that makes faux (fake) wasps hives.

http://www.amazon.com/Firemaster-00900-Natural-Deterrent-2-pack/dp/B000W93LUU

Cost is around $10 and it works. But you do have this funky/ugly fake wasp hive on your building...but no hornets. Hope that helps, Nadja Dee Witherbee Seattle, WA

A quick google search pulled up a couple of options:

http://www.greenpestservices.net/services/pest-control

This site specifically mentions wasps in their common pests page.

http://www.cascadepest.com/about/why-cascade.htm

This site seems to cater to the "sorta green" crowd.

http://www.alphaecological.com/green/

This company appears to focus mostly on prevention in the first place.

Hope those were helpful!