If you're concerned about the environment, what about helping on a conservation project abroad? 

The organisations listed in this section are not necessarily endorsed or approved by do-it.  You should research organisations carefully before making any commitments.

Azafady 

Community-based conservation and development in Madagascar.

Blue Ventures 

Marine conservation in Madagascar.

BTCV 

Wide variety of 'conservation holidays'.

Concordia 

A range of 2-4 week community based environmental and conservation projects in over 40 countries worldwide.

Coral Cay 

Reef and rainforest expeditions in the Philippenes, Papua New Guinea and Tobago.

Earthwatch 

Over 140 conservation research expeditions in 50 countries around the globe.

Fundacion Golondrinas 

Help conserve the ecosystem of Ecuador with local people. (The organisation is based in Ecuador) 

Global Vision International

Environmental and community projects in South Africa, the USA and Asia.  (They are a registered company with an associated charitable trust.)

Greenforce 

Conservation expeditions everywhere from Borneo and Fiji to Zambia and Peru.

i-to-i 

Projects in 23 countries worldwide: teaching, conservation, care work, building, and work experience.

Raleigh

quick search