The American Chemical Society has a Career Navigator website:

http://www.acs.org/content/acs/en/careers.html 
and the C&EN Jobs site:
http://chemistryjobs.acs.org/jobs

Joel Walker maintains The Medicinal Chemistry Jobs List.

New Scientist hosts the ChemJobs website:
http://www.chemjobs.net

LinkedIn has jobs:
https://www.linkedin.com/jobs/

Argonne National Lab

Brookhaven National Lab

Department of Energy

Fermilab

Frederick National Lab (NCI)

Idaho National Lab

Jet Propulsion Lab

Lawrence Berkeley National Lab

Lawrence Livermore National Lab

Los Alamos National Lab

NASA

National Academy of Sciences

National Government Lab

National Renewable Energy Lab

National Science Foundation

Oak Ridge National Lab

Pacific Northwest National Lab

Sandia National Lab

Smithsonian Environmental Research Center

Smithsonian Institute

Smithsonian Marine Station