This is one I like extra much, simply because I was the one to take it. It contains more memories than a better picture from a random show would contain, and is therefore more valuable to me. This is taken at Nightwish's last show on their DPP-tour, at Hartwall Areena 19.9.2009. Doesn't she look a bit like an angel? ;)
Another one I'm extra attached to is this one from the band's show 1.1.2008 at Jäähalli in Helsinki.