There are also the Bible accounts of Job, in the gospels with Jesus in the wilderness, in Revelation his being thrown out of Heaven to the vicinity of Earth, as some of the very obvious ones that proves Satan is real and active. (There are many, many more scriptural examples.
As far as I know there are only Christadelphians (sp?) who don't believe Satan is real, for some bewildering reason.
I was just flicking through looking for an old post I'd sent when I discovered this... I must have posted this comment in the wrong thread...oops!