Here's a handy list of calculators and resistors selectors from our friends over at CEPD.
There is a 1% resistor finder, resistor divider, resistors in parallel and RC time constant calculator found in the Resistor Calculators.
There are microstrip impedance and differential impedance used for USB traces found in the microstrip calculators.
There are line of sight VHF, power conversion and VHF signal loss found in the transmission calculators.
Time Conversion Calculators
Splitter and Attenuator Calculators
Find resistor values for Y splitter, T attenuator or Pi attenuator that can be found in the splitter and attenuator calculators.
Power Conversion Calculator
Conver voltage, dBm, dBu, dBV, or power to another form for a given impedance and waveform type in the power conversion calculator.
ASCII Character Chart
ASCII Character Chart that shows the symbols, hex values, octal values, decimal values, binary value and description of the character.
EIA232 Reference Chart
EIA232 Reference Chart that shows the pinout and signal names for DB25, DE9, and RJ45 connectors.
1st Order Filter Calculators
1st Order Filter Design for lowpass and highpass filters. The calculators create analog component values, analog and digital filter coeffiecients.
2nd Order Filter Calculators
2nd Order Filter Design for lowpass, highpass, bandpass and bandstop filters. The calculators create analog component values, analog and digital filter coeffiecients.