The Gospel of Matthew has Jesus ride on two donkeys as he enters Jerusalem, is, in my mind, a pretty telling contradiction. Mark and Luke have Jesus riding on a colt, Matthew has him riding on an ass and a colt. The author of Matthew is obviously cherry-picking the Old Testament for prophecies and stumbles on a mis-translation in the Septuagint. There other instances in Matthew cherry-picking the Old Testament that are telling as well.
The day Jesus is crucified is a good one too. Mark (and I think the other synoptics) have Jesus crucified on the day after Passover (the Passover meal being the genesis for the Last Supper). The Gospel of John has him crucified the day before Passover. Apparently the reason John does this is to support the comparison of Jesus as the sacrificial Passover lamb ala Exodus, something the synoptics apparently aren't interested in. Also in John the Last Supper has nothing to do with the Passover meal. Biblical scholar Bart Ehrman uses this contradiction prominently in his deconstruction of the Gospel of John.
Also, for a good comprehensive list of contradictions, check out the Skeptic's Annotated Bible.
http://www.skepticsannotatedbible.com/contra/by_name.html
ABE: I meant to suggest simply reading the Gospel of Mark. It's not that long. There are so many stories of Jesus casting out demons it is startling. The book is rife with what these days would be described as superstition.
Edited by Clark, : No reason given.