ACBAR (Agency Coordinating Body For Afghan Relief) has a web site that lists jobs in Afghanistan by a variety of NGOs. Most jobs are for Afghan nationals, but there are some for international consultants:
www.acbar.org

UNDP Afghanistan has job listings here:
http://www.undp.org.af/jobs/default.htm

UNAMA Afghanistan lists jobs in Afghanistan here:
(most are for Afghans, however)
http://www.unama-afg.org/va/vacancies.htm

UNFPA will be undertaking the official country census next year:
http://afghanistan.unfpa.org/

US Federal jobs in Afghanistan are here:
http://federalgovernmentjobs.us/job-location/afghanistan.html

Many organizations in Afghanistan use ReliefWeb to recruit international consultants:
http://www.reliefweb.int/

And some Afghan organizations are seeking help from online volunteers:
http://www.onlinevolunteering.org