Aid/Development work

Hi,

Im trying to get out to central/south america to volunteer in aid/development work. Im looking for long term projects in the hope that eventually one day may lead to paid employment with experience and contacts.  I know of many organizations that offer volunteer placements for a few months in orphanges, schools etc but if anyone knows of anyone, any place or anything that offers more long term development work I would be more than grateful if you let me know.

Thanks in advance