Fusion and Plasma Science:

Coalition for Plasma Science
GA Fusion Education
FUSEdWeb
Ippex online
MIT Plasma Science and Fusion Center

X-ray Photoelectron Spectroscopy and database

Surface Science Tutorial
UK surface analysis forum
Wikipedia
NIST XPS database
LaSurface.com
X-ray data booklet
NIST Chemistry
XPSdata.com

Auger Electron Spectroscopy and database

AES Wikipedia
Lasurface.com
UK Surface Analysis

Low Energy Ion Scattering Spectroscopy

Wikipedia
Calipso

Spectroscopy database

Photonics Calculations
NIST Atomic Spectra database
http://www.pmp.uni-hannover.de/cgi-bin/ssi/test/kurucz/sekur.html
CRC Handbook of Chem & Phys
Handbook of Basic Atomic Data (NIST)
Ionization energies
Stark broadening parameters
X-ray data booklet
X-ray interaction with matter
Kelly EUV/X-ray Spectroscopy database
NIST
Photon Cross-section database
X-ray transition energies
X-ray attenuation
Optical Constants
Atomic and Plasma database
NIST Atomic and Molecular Physics
Ground levels and Ionization energies
Electron impact ionization and excitation cross-section
Blackbody curve

Material Properties

Webelements
NIST
Matweb
Matter Glossary
Virtual Material Center
Elemental data index
Perioidic Table - Technical data for elements

Laser Physics and Photonics

Encyclopedia from RPP
Newport
Optics On-line assistant
Melles-Griot  
The virtual Physics Center
Optical Calculator
Eric Weisstain’s world of Optics

Thermo-couple database

NIST

General Physics

Physical Constants
Atomic Weights and isotope compositions
Database for atoms, molecules, gases and plasma

Nuclear Database

National Nuclear Data Center
Nuclear Arsenals