This has probably been asked and answered before, but I'm trying to remember all the times Harry has opened his third eye to see things and people as they really are.
Storm Front - Harry looks at Victor Sells house with the Sight. Did he use the Sight earlier in the book? I don't remember.
Fool Moon - ?
Grave Peril - Harry sees Mavra at Bianca party, but I think he just sees her standing on the stairs above him, he doesn't look at her face. Earlier, Harry sees Mickey Malone and Murphy with his sight.
Summer Knight - Harry sees both Mab and Titania with his sight. It floors him.
Death Masks - ?
Blood Rights - ?
Dead Beat - Harry looks at the murder site at the Field Museum.
Proven Guilty - Harry looks at the bathroom where the assault took place that Nelson was blamed for.
White Night - ?
Small Favor - ?
Turn Coat - Harry sees the naagloshii. It floors him and makes him feel sick afterwards.
Changes - ?
Ghost Story - Does this book even count because Harry wasn't really himself? I think ghost Harry tried to use his Sight to look at an angel, but was blocked from doing so.
Cold Days - ?
Skin Game - ?
I know that in one book Harry looked at Murphy again with his sight, but I don't remember which one. Has Harry looked at anyone else that I'm forgetting?