This might be a little tougher for you to follow, but every major city has races that support the green movement. Whenever possible, support these races. You might question, how I know if a race is a green race? Send an email to the race organizer. If they get enough of these inquiries [and believe me they do] they start making subtle changes to do what they can to eliminate those items such as 'medals' that are actually engraved wood, running results computers that are solar powered, running goody bags that are recycled and can be used over and over again for shopping, and a recycled shoe drive where you can deposit your old running shoes.
If you are looking for a race that can give you a blue print on what they can do to go green, I am including a link to the most environmental friendly race we have here in Minnesota: http://bit.ly/fc5fxJ The Urban Wildlife Half Marathon & 5K supports the use of all those efforts I've listed above and more. Their running numbers last year were made of a bio degradable material that could be planted for sun flowers. Okay, I'll admit, the rain last year rode havoc on the number staying on us during the race, but the point is they are trying different efforts in an attempt to have runners not leave an environmental footprint in the races we run.