Listen to her cover of Peter Gabriel's "Darkness", then (if you haven't already), listen to the Peter Gabriel original.
Depending on your taste, "Still Of The Night" originally by Whitesnake.
Nightwish has rarely performed its own cover of "Over the Hills and Far Away" by Gary Moore since Tarja was kicked out of the band. Tarja performs it all the time.
There is a small yet growing rivalry between Tarja fans and those of American band Evanescence. Evanescence singer Amy Lee Hartzler could very well be a younger sister of Tarja. However, most fans of one singer do not generally know of the other right away.
Les Yay: Tarja and Sharon Den Adel in the video for "Paradise (What About Us?)" They give each other longing looks, smile coyly, stand really close to each other (to the point where Tarja's hair keeps blowing in Sharon's face)... And it all culminates in the two of them dressed in flowing gowns, holding hands and singing to each other.
They have a ship name now - Sharja - and quite the fandom, with fanart◊, fanfiction... Anything and everything!
Slasher Smile: Tarja shows a rather convincing one in the "Victim of Ritual" video.