I use open D (D A D F# A D) for songs like Joni Mitchell's 'Big Yellow Taxi' - it's a lot more resonant for bashing chords (I've got a LOUD voice). I know Joni used open G, but D suits me better.

It's also useful if you want to experiment with 'slide' guitar - a 'Canada Dry' bottle works well.

The advert also sums up my life's ambition - 'Drink Canada Dry'...

Ooops! Thread creep!