This really only applies if you have any keyboard knowledge, but I suggested it to someone I know, who's getting some results, so someone else might benefit.
For those who've played keyboard or piano, you'll know that each octave is laid out exactly the same. All of the altered tones (sharps and flats) are black keys, while all the named notes are white keys. And there is a pattern, from middle C, the next set of sharps (C sharp, and D sharp) are close to one another. Then there is a gap, as E and F are next to each other (two white keys), then F,G, and A sharp are grouped in 3. Then B and C are white keys next to each other, then the whole thing repeats.
Well, the proposition is to get a magic marker, (permanent), and ruin a set of strings on an old guitar, by marking out all the sharp notes with a black dot on each string. Now when you look at the guitar, it is laid out like a set of keyboards. Where the patterns are similar on each string, the notes are the same. All the black marks are sharps, and all the frets without are named notes. And if you are looking for the name of a note, look at where it sits on the pattern, and think of the key on a keyboard.
Like I said, I thought this up for someone else, but they've had some success, so I thought I'd share.
Feedback (from anyone who gives it a go) would be lovely