Well, two instrumentals that I'd like to learn are "Sleepwalk" by Santo and Johnny, and "Sweet Georgia Brown" (similar to way the Django played it or was done by Old and in the Way with Vassar Clements on fiddle, I think Doc Watson might have done a version like this too). I'm not sure how well "Sleepwalk" would go over at a wedding (I think it would be cool if maybe a bit slow). I'm also not sure how a solo
slide version of "Sweet Georgia Brown" would work; it's a song that might really need accompaniment to give the chordal support since that melody line really flies by.
Now if I were to play slide at a wedding, I'd go for the faster blues songs (with all the sexual overtones), but I think these need to be sung as well. I'd be playing "Rollin' and Tumblin'" by Muddy Waters and "Shake Your Moneymaker" by Elmore James. In fact, Elmore James has a lot of high energy blues stuff.
I'd also be tempted to play "One Way Out" as the Allman Brothers did. "Cause there's a man down there, might be your old man I don't know." What better song to celebrate a wedding, eh?
Oh, in the same ilk as "Sleepwalk" I'd also look at the Hawian guitar song which I think is called, "Aloe ah oi" (I'll see if I can find it today and make sure that's the title).