EngineerSupply.com
Resource for engineering tools and supplies.

Fridgetech.com
This is a commercial site which contains lots of data, information and calculators on industrial and commersial refrigeration. VERY GOOD!

Metals weights calculator from Maryland metrics.
Maryland metrics offers this free calculator in metric. In their site you can find other calculators and tons of information. EXCELLENT!

Monachos engineering calculators.
A collection of powerful online engineering calculators and resources. Unit conversion , voltage drop , pipe friction loss , data tables and more...

Resistor color code
A website dedicated to resistor color codes. Convert resistor code to numerical values.

Venturi flow calculator.
This is a free online venturi calculator. EXCELLENT!

engineerstoolbox.com
The site provides a great beam calculator which calculates every kind of beam dimensioning problem.