Topic: Drop A!
I was coming up with my own arrangement of a song to play at church (He's Ever Over Me, if any one knows it) and I didn't have any music, chords, etc, so I figured out the melody by ear and discovered that it was based on an A chord. I wanted to have a nice low bass note to play in between chords and melodies, so I experimented with drop D, but found out that it just didn't sound right. I tried standard tuning but the low E didn't have the sound I wanted. After that didn't work, I tuned the bottom string to a full octave below the 5th string A (this is a standard scale Martin here). Wow, does that ever sound cool! I didn't think that getting the 6th string down to an A would be possible. Anyway, a long-winded post, I know, but if you want a really deep bass note between chords, try A if you can hit it.
Switchfoot