"All For Laura" from The Woman in White. Especially the Reprise. "I will live to right this wrong!" and the way those notes are held is absolutely amazing <3
http://www.youtube.com/watch?v=v76IR69CKpY All I got to listen too till the cast recording is bought, but still amazingly powerful live. That's my favorite part of musical theater, the people can sing INCREDIBLY WELL live(most times, better than on a recording)