If you use OS X, cmd+click. Cmd+click even works on some things that middle click doesn't, for example middle clicking on the home, back/forward, or top sites

If you use OS X, cmd+click. Cmd+click even works on some things that middle click doesn't, for example middle clicking on the home, back/forward, or top sites buttons in Safari will do nothing at all, but cmd+clicking will properly open your home page, previous page, or top sites page in a new tab.