Dan, what you need is The Circle of Fifths, preferably one that has two circles, the smaller on a pivot inside the larger. The circle itself has these chords: C-G-D-A-E-B-F#-C#-G#-Eb-Bb-F wrapping around it evenly spaced, with the F jumping to the original C to complete the circle. With this circle on the outside on a stationary card and the same but smaller circle on the inside on a rotating card, you can transpose from key to key quite easily:
If you want to transpose from C to G, for example, you rotate the inner circle so that the C lines up with the G; all the other chords in the music will then line up with the appropriate chords in G.
The circle is reproduced in many instrument instruction books, and probably can be purchased seperately on hard stock from any good music store. Just ask for The Circle of Fifths (it also has other uses, and is one of the most important tools for any musician).