My standard slide tuning is DAFFAD. It's really nice for some cool droney bits and does a faux 12 string with the Fs in the middle. Good for blues and really pretty all round.
John Butler uses some crazy tunings, might want to check his flow man.
Keith Richards used "open G"(DGDGBD) for songs like "Honky Tonk Woman", "Brown Sugar", and many more. He learned it from Ry Cooder. Bonnie Raitt uses the same tuning up a whole step to make "open A"(EAEAC#E) Muddy Waters and Robert Johnson also used this tuning as well as others.
"Open D"(DADF#AD) or "Open E"(EBEG#BE) is the Elmore James "Dust My Broom" tuning. Also used by Muddy, R. Johnson, and Hound Dog Taylor.
DADFAD pronounced Dad-Fad is used by a lot of songwriters without a slide and can give a droning celtic vibe.
I had the same problem once and bought an old lap steel and metal bar. It was easier than trying to play slide. If you get a really heavy bar you want have to push down with a lot of pressure which helps too.
I believe Keith actually uses 5 strings, no bottom E; hence his methodology, "five strings, three notes, two fingers and one arsehole to play it". I've certainly never heard the bottom D on Stones records but I may just not be that well trained. Having tried it myself the low D muddies his riffs up and makes the lowest note a 5th which isn't too helpful.
Personally, I like open G but leaving the bottom E as E (EGDGBD). As it's the relative minor you can get some nice voicings come out with it (but don't use the string all the time!)
Also look at this...
DGCGBD - it's open G with a dropped D string to C, very nice and spatial. It's actually banjo open C tuning but on a guitar.