Additional evidence is provided by gravitational lensing observations, the most spectacular of which is the Bullet Cluster: http://apod.nasa.gov/apod/ap060824.html

Dark matter is not needed to explain the rotation of galixies. http://arxiv.org/abs/1007.3778 Assuming that paper is true, dark matter is not the simplest idea and by Ockham's razor, we should drop dark matter as known today.