The fretboard below shows the location of every note that occurs in a given chord along the length of the fretboard. In the dropdown menus underneath the fretboard, you can select which chord's notes you want to display. Here you can specify (i) the root note, (ii) the type of chord, and (iii) the tuning that the guitar is in.
The fretboard below shows the location of every note that occurs in a given scale along the length of the fretboard. In the dropdown menus underneath the fretboard, you can select the key for which you want to display a scale. Here you can specify (i) the root note, (ii) the mode of the key, and (iii) the tuning that the guitar is in.
The table below displays the seven chords based on a given key/scale. In the drop down menu you can select the root note and the key (major or minor) for which you want to display the chords.
Chords based on C Major:
Here's a nice program from the MusicTheorySite for going in the other direction: determining the key on the basis of a chord progression.