MatWeb
Materials Properties data

AZoM
AZoM is a knowledge tool intended to provide the design and engineering community with a source of all the information needed to make an informed decision on material selection.

Crystal Lattice Structures
Index of common crystal lattice structures

Materials Properties and Data (NIST)
Materials properties and data listed by property and materials class

Structural Ceramics Database (NIST)
Evaluated materials property data for a wide range of advanced ceramics

High Temperature Superconducting Materials Properties (NIST)
Thermal, mechanical, and superconducting property data for oxide superconductors

Thermochemical Databases
Thermochemical Databases and Models for High-Temperature Materials Processing, Combustion, and Corrosion

MEMS Materials Data (MEMS Clearinghouse)
Property data for materials used in MEMS

NIST Chemistry Webbook (ChemWeb and NIST)
Chemical and physical properties data for a variety of compounds

Chemistry Compound Search (ChemWeb)
Text or structure searching of ChemWeb's structure database

ChemFinder
Chemical database with physical properties, structures, and links to sources and properties

Physical Reference Data (NIST)
Various physical data including physical constants, spectroscopic data etc.

WebElements
Periodic table of the elements

Electronic Structures Database
Database of electronic structure calculations for various elements and structures.

Reference Data for Electronic Structure Calculations
Evaluated reference data for electronics structure calculations, from NIST.

X-Ray Interactions with Matter
Data for x-ray interactions for various elements and compounds

Engineering Statistics Handbook (NIST/Sematech)
E-handbook of statistical methods

Isotopes (LBL)
Table of isotopes

MEDLINE® Database
Produced by the National Library of Medicine, covering fields of medicine, nursing, dentistry, veterinary medicine, the health care system and the preclinical sciences.

Online Engineering Calculators (Martindale's Reference Desk)
Various online engineering calculators and resources