Open D tuning is used a lot in slide guitar. "Open E" is the same relative tuning, but every note would be up one tone from what is shown below! The problem with Open E is that you have to tune strings up, where with Open D you just tune them down... use a capo on 2 to get to Open E!

It's pretty easy to get going, just tune strings 6, 2, and 1 down one tone and string 3 down a semitone.

Open D Tuning

String	6	5	4	3	2	1
Tuning	D	A	D	F#	A	D

Some songs using Open D Tuning:

??? my mind has gone blank!!! but there are loads!!

Please suggest more on the forum link below... I'm having trouble thinking of them now, but there are many!