Recently redesigned gateway to scientific resources produced by the U.S. government. There are a number of important chemistry-related databases available here, including ChemWebBook, CHEMIDPlus, IRIS, CancerNet. etc. Many are searchable by compound name, CAS Registry Number, structure, etc.
Science Accelerator is a gateway to science, including R&D results, project descriptions, accomplishments, and more, via resources made available by the Office of Scientific and Technical Information (OSTI), U.S. Department of Energy.
Access to over 210,000 full-text documents and bibliographic citations of Department of Energy (DOE) research report literature. Documents are primarily from 1991 forward and were produced by DOE, the DOE contractor community, and/or DOE grantees. Legacy documents are added as they become available in electronic format.
Full-text access to a host of resources published by the Institute of Electrical and Electronics Engineers (IEEE) and affiliated societies. Find articles, conference proceedings, transactions, etc. The Conference section can be particularly fruitful on nanotechnology topics.
Open access to 600,000+ e-prints in Physics and other areas--given the close interface between chemistry and physics in materials science, particularly, you'll find relevant materials here. Note that articles undergo revision based on comments submitted to the site following initial posting. This is site is particularly interesting since it demonstrates how scholarly communication practices are evolving and are no longer focused entirely on journal literature as in the past.