AAS Job Register - http://jobregister.aas.org/
SPIE Career Center - http://spie.org/x37648.xml
The Chronicle of Higher Education Jobs listing - https://chronicle.com/section/jobs/61
The US Government's Official Job site - https://www.usajobs.gov/
Other resources:
Jobs for Astronomers and the facebook group can be found here https://www.facebook.com/groups/158795700924588/
From Alaina Levine:
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Articles about marketing your value and finding opportunities in the postdoc - Science Careers