Ive recently started putting all of my components into a database but over the years, ive collected a lot of spare components that i can no longer remember the values/ ratings of, ive recently found a web site which has a central collection of known datasheets, this is:- http://www.datasheetcatalog.com/
Just look on the component for any identifying numbers/ letters and enter them into the search bar. Ive only stumped it on a few components, and was impressed to find that mosfets and transistor companies seem to use the same identifying tags for the same value devices.
and for those how cant be bothered working out resistor values for yourself :http://www.samengstrom.com/nxl/3660/4_band_resistor_color_code_page.en.html
This has links for 4 - 5 - and 6 colour bar resistors
Capacitors generally seem to have their property values stamped on them so no problem there.
Ive just spent 2 hours working out the correct wires / sequences for 4 different stepper motors, since stepper motor data seems difficult to get hold of, now ive got the colour codes and sequences correct, i just need to use an mcu to calculate fastest and slowest rise/fall times.
p.s. a also had to work out how many steps they took to make a full circle, by tapping the wires in sequence until it finally came all of the way around.... how annoyed can you get when you tap the wrong wire for the 6th time