ChemFinder.com
Type in a chemical name, formula or molecular weight to receive chemical property data and plentiful links to toxicological, regulatory, health, usage and ordering information.

Engineering Units Conversion Calculator
If you can read the font, this tool by Process Associates of America offers simple units conversion for a wide variety of engineering measurements.

Fuel Energy Conversion Calculator
Units converter between crude oil and natural gas.

Hydraulics Calculator
LMNO Engineering, Research and Software provides a single-page collection of calculation tools for hydraulics and engineering reference for a nominal $8 registration fee.  Unit conversions, open channel flow, pipe flow, ground water flow and more.  Some calculators are freebies.

Periodic Table
WebElements provides a colorful online periodic table with detailed property and usage information for each element.

SIC / NAICS Industry Classification Codes
Search for an industry code, convert SIC codes to NAICS (or vice versa) and view category data and descriptions.    

Units Converter
Another handy units conversion tool. Select your parameter, choose the desired conversion and enter your number for an answer within seconds.