I'm about to order a bunch of capacitors to keep on hand. What are some commonly used values I should stock up on? I know 0.1uF are good to have for decoupling, but what about others?
Just buy one of those packs of assorted capacitors that are generally available (they usually have 10 of every value), and replenish the individual values that you find yourself using the most.
As the selection of the capacitors varies from application to application.
It actually depends on where we are using this capacitors. I'll give some list of capacitors and its values and place of applications.
Ceramic Capacitors: Generally these have high temperature stability and works at high frequencies.
Values are generally available from a few pico farads up to around 0.1uF.
Electrolytic Capacitors: This type of capacitor offers a very high level of capacitance and the maximum frequency that can operate is 100Hz.
Silver mica Capacitors: They offer a high degree of performance for radio frequencies and in particular they offer a low temperature co-efficient (typically around 50 ppm / C).
Although expensive they are ideal for applications such as filters and RF oscillators.
Tantalum Capacitors: It has exceedingly high levels of capacitance and very sensitive of thermal runaway.
Electric double-layer capacitor (EDLC): These are also known as supercapacitor, supercondenser, electrochemical double layer capacitor, or ultracapacitor.
It's an electrochemical capacitor with relatively high energy density.
Their energy density is typically hundreds of times greater than conventional electrolytic capacitors.
A variable capacitor (also known as a "variable air condenser"): is a capacitor whose capacitance may be intentionally and repeatedly changed mechanically or electronically.
Variable capacitors are often used in L/C circuits to set the resonance frequency.
The values/types will somewhat depend on what kinds of stuff you are designing, but here's an attempt at an answer:
100nF ceramic, lots and lots of. Also now ceramic caps have improved and become cheaper, you can use them to replace electrolytics up to ~10uF.
Mouser do some real cheap large ceramic values.
For lowish speed (say up to 40MHz) the above should do fine. For higher (e.g. fast micros, FPGAs, etc) you would need:
1uF ceramic - lots of. (100nF ceramic) 10nF ceramic - lots of. Possibly 1nF ceramic lots of too, depending on the manufacturers advice.
Crystal bypass caps:
15pF, 20pF, 30pF ceramic. For typical microcontroller crystal oscillator (or a discrete inverting gate version)
Grab a few in the range from 100uF to 1000uF, make sure the caps voltage rating is suitable for your circuit. Double the rating is good (e.g. if circuit runs at 5V then use >10V rated) For audio you may want a quite a few 10uF, 22uF, etc tantalum/Al and also some non-polarised electrolytics. If working with power amp output stages then high quality e.g. 1000uF electros may well be needed, depending on power supply (single/dual rail)
Plastic film, Mica, etc:
If you are working with sensitive audio/RF analog circuits then you will likely need a decent range of stable/good quality capacitors. Probably best to order these as required.
If I think of any more I will add them..
Other caps I would play by ear mostly. You will almost certainly end up using a few of each value ceramic from 10pF up to 1uF if you are busy, but since you can very quick delivery nowadays you could simply see what you use most (e.g I get next day delivery with an order up to 8pm) You will quickly build up a good range either way.
Tantalum are exceedingly sensitive to destruction by overvoltage.
In any "high energy" circuit where ANY spikes or small surges occur that are in excess of rated voltage by more than about 10% a tantalum capacitor will probably be destroyed. "High energy" is any power supply or similarly current rated circuit.
Solid Aluminum have about all the advantages of Tantalum but do not fail catastrophically under modest over-voltage.
Polystyrene. Large per capacitance. Precision - used for %high stability parts for filters etc.
Polyester / Film.
I'll try to add to this list if I get time.