Half-Blood Prince is No. 5 on Yahoo! Movies Top 10 Most-Viewed Trailers of 2009
The top spot went to Twilight: New Moon, followed by Transformers: Revenge of the Fallen, 2012 and Terminator Salvation, respectively.
These rankings are based on video streaming numbers on their website. The top two films got over 20 million views apiece. Thanks to Emily for the tip!