Johnny Winter was pretty hot on slide and some of the old blues guys like Fed McDowell had their own unique style of slide playing too.
I played a couple of gigs at Dundee a couple of years ago with a wee Canadian guy called Jimmy C. Jimmy is just something else on guitar and a pretty good slide player as well. One of his tricks was to take a glass of booze out of someone's hand and use it to play a slide solo. Amazing wee guy.