During the last little while, I have become aware of a group called the Earthwatch Institute which has an interesting approach to participating in environmental research and the promotion of sustainability. Since 1971, they have linked more than 80,000 volunteers to more than 2,500 different research projects. The volunteers contribute both financially and through their labour, in exchange for which they get to see some amazing places, meet and work with scientists, and generally gain a better understanding of the world. While you have to wonder how helpful non-specialists could actually be during such a project, it does sound like it would be fascinating.
If you have always envied the people zipping around on helicopters or piloting ships through Antarctic waters, this might be your only opportunity, short of becoming a research scientist. Right now, they are organizing expeditions to Alaskan glaciers, the Amazon river basin, coral reefs in the Bahamas, and a number of other places besides. They seem to cost about $2000-3000, not including travel to the location in question.
For those without scientific training to go on such expeditions may be a bit touristic, but I can see how it could contribute valuable resources to projects – particularly those involving scenic places and photogenic animals.