Bernard Bolzano is an often overlooked if not forgotten philosophical titan of the 19th century. Much of Bolzano scholarship is published in German and left untranslated. His cosmological argument for a being with unconditional existence elegantly sidesteps all of the objections to traditional, Thomistic-Leibnizian style arguments for an absolutely simple being. And, like so many philosophers of old (relatively speaking), Bolzano is highly relevant to the current interest in grounding.
Side note: One interesting side effect of this ‘ground swell,’ if you will, is that it has contemporary analytic philosophers rediscovering the dusty annuls that usually occupy the shelves of historical philosophers. Or, an alternative way of looking at it is this: the current interest of analytic philosophers in historical scholarship relevant to grounding dispels the myth that they are ahistorical bores. One could make the same point apropos the current revival of neo-aristotelian metaphysics, if the ground swell isn’t just symptomatic of this revival.