1) Stay in G tuning, playing in the key of C, and then capo up two (key of D) or four (key of E) frets. The most common chords in the key of C are C, G, and F; all of which lend themselves to melody playing. Chordal style backups are also fairly easy when playing in the key of C out of G tuning.
Listen to the following song examples (Tabs are available on my main page):
2) Switch to Open C or Double C tuning and then capo up two (key of D) or four (key of E) frets. Open C tuning is a very useful tuning when you need to provide a "chordal" style backup as well as doing some melody work. Double C usually is the tuning of choice when playing flowing melody line, such as you find in "fiddle tunes", but doesn't seem to lend itself very easily to "chordal" style backups.
Listen to the following song examples (Tabs are available on my main page):
3) The last solution is for the key of E only...
Add a "Long Neck" banjo to your collection! You will need to get comfortable playing out of the "open neck" in G tuning (which would now be transposed to the key of E). This is not an easy task unless you have long arms and fingers. My fingers are very short and it took me months before I began to feel comfortable with those extra three frets...
Thanks... Mike