Open D tuning, while covered in open tuning, deserves a node of its own, in that its possible uses - and small drawbacks, I guess - also deserve to be looked at. Starting from the top string, the low E, this is the re-tuning:

E -> D
A -> A (no change)
D -> D (no change)
G -> F#
B -> A
E -> D

This tuning is great for experimentation and slide guitar. There are several songs I can think of off the top of my head for which this tuning is used. She Talks To Angels, by The Black Crowes can use open D tuning, and is perhaps healthier on the strings than open E tuning, as there is no tuning up of strings to be done. All you've got to do is use a capo up two frets. In this case, however, it's possible you may get some rattling of the strings along the fretboard as you attempt barre chords along the nine and twelfth frets, no matter what weight of strings you're using.

This tuning is common for Jimmy Page to use, and it's used in a couple Coverdale/Page songs, as well as some Led Zeppelin songs.

The instrumental piece The Badger, by The Tea Party, can be played in open D tuning, though I prefer to use drop D tuning for it - it makes bending your fingers at impossible angles a little less bizarre and painful. In the songs Angel Standing By, and Daddy, by Jewel, she employs open D tuning.

All in all, open D is a very versatile and fun alternate tuning method, for just about any guitar player, though I would suggest having medium-light to medium gauge strings, as all the tuned-down strings can rattle, and may hit the fretboard in the case of some higher barre chords, as I've mentioned above.