Really good Fanvids/music videos on YouTube.
Nightwish reaction videos on YT. When the YTer puts on 'Ghost Love Score' (Wacken 2013), says, "I've never heard of this band, let's see what they've got," and ten minutes sitting there with their jaws on the floor, having gone through a range of gestures (raised eyebrows, "Wow!", "Jesus!", devil horns and air punches, then a range of shock and awe gestures when the singer hits her final note). By watching their reactions, I get to relive the awe I felt when I first saw them.
I love watching geeky vids like super heroes set to I Need a Hero and vids of people watching stuff for the first time way too much.