Many conclusions will borrow from a combination of the above techniques. A fund-raising presentation I attended had a three-part conclusion: It started with a summary of reasons why the cause was especially worthy and led into this quotation from Ralph Waldo Emerson: "No man can truly help another man without helping himself." The speaker then launched into a direct appeal: "So please reach into your hearts and checkbooks so that tomorrow really will be a better day for the needy."
These techniques also apply in general communication. For example, after a meeting with a client you might need to sum up your discussion or ask for the order. Never let important conversations or discussions just drift away.
Whatever technique you use, strive for a conclusion that will stay with your listeners long after they leave their seats and return to their private lives.