Kadri is the main one for the Leafs. He is better than Kerfoot, which is all that is left of that trade for the Leafs. I would undo it in a minute if I had the chance.
Carter Verhaeghe would come in pretty handy now too, but I don't think anyone could have know what he would be when he was traded. It's hard to work up too much seller's remorse over that one.
A few years ago there were a lot of active former Leafs I would have liked to have back, such as Anton Stralman, but they are all getting older and/or retired, and there's not a whole lot of value out there that would still compete for spots on the Leafs' roster at their current price-points.
Phil Kessel, Kasperi Kapanen, Andreas Johnsson, Connor Brown, Nikita Zaitsev, Richard Panik and Curtis McElhinney are all still very useful NHL players, but none of them would fit into the Leafs plans at this point in time.
McElhinney would have been a Godsend during the Leafs' backup-goaltender crisis that has now passed, and I can't think of anyone other than Kadri and Verhaeghe that I now wish were back on the roster today.