The third featured preview from
Half-Blood Prince courtesy of ABC Family focuses on the new Potions Master, Horace Slughorn, and includes interviews with Dan Radcliffe, Rupert Grint, David Yates, David Barron and, of course, Jim Broadbent. It can be seen below:
Source:
Oclumencia
UPDATE: Screencaps for the third preview can be seen
here: