Wow, there are at least several on this list that I haven't heard of. Since I like the ones that are listed which I have heard, I know I will need to check these other guys out. (though I'm surprised that it took so long to get Johnny Winter on that list)
I'll just add some names which I haven't seen here yet. Not my very top guys neccessarily (who may already have been listed in this thread) but should be known by sliders:
Larry "Rhino" Reinhardt
Hard blues rock -- Captian Beyond and Iron Butterfly, Metamorphosis album. He was in Dickey Betts pre Allman Bros. Band group which I think was called The Second Coming. You can hear that southern style, but very hard.
Sister Rosettta Tharp
Bill Harkleroad aka Zoot Horn Rollo
Captain Beefheart and the Magic Band classic line up from Trout Mask Replica and Clearspot. Delta/Chicago blues via Stravinsky and Ornette Coleman.
Jeremy Spencer
Peter Green's Fleetwood Mac. A great mimic of many classic blues players; especially Elmore James.
Quicksilver Messanger Service (was it John Clipollina or the other guy?) I've always thought these guys (and other 60s SF guys) might have been the link between Elmore James playing and the almost unprecedented
slide of long extended jams of the Allmans.
Reverand Gary Davis
(I hope that's the guy I'm thinking of)
Barbecue Bob
(again, I hope that's the guy I'm thinking of)
Leslie West
Mountain. He rarely plays slide but his version of Crossroader from the live album "The Road Goes Ever On" is pretty nasty.
Michael Bloomfield
Such a great player overall, I think his slide work is often overlooked.
Mick Taylor
I really love his slide with The Stones, like "All Down the Line" and "Love in Vain" but he is great on the Mayall 70th Birthday Concert DVD
I'll think of a few more later.