This page holds some info on available M.Sc., Ph.D., Post-Doc and faculty positions
As the notices for these positions change on a daily basis this site only offers links to other sites that regularly update this information.
A very good e-mail list serve for ecologist is Ecolog, which you can sign up to and also see all of its listings together. It also posts many notices about available Ph.D., Post-doc and faculty positions.
Another excellent site for information on jobs, post-docs etc. is that of the Ecological Society of America which links to a multitude of other sites.
A site with various volunteering, graduate studentships and job opportunities is Earthworks-job, which has a page dedicated to ecology,conservation, biodiversity or restoration jobs.