A passage in the Qur'an that's upheld as an example of Islam teaching peace is Sura 5 (the Table) verse 32. It states "if any one slew a person -- unless it be for murder or for spreading mischief in the land -- it would be as if he slew the whole people: and if any one saved a life, it would be as if he saved the life of the whole people."
The Corner recently raised two interesting points about this passage. First, this idea is not original to the Qur'an, but forms a part of the Babylonian Talmud, written in the 2nd century (and recording traditions that pre-date that).
The second interesting point about this passage is that the verse following it, 5:33, states, "The punishment of those who wage war against Allah and His Messenger, and strive with might and main for mischief through the land is: execution, or crucifixion, or the cutting off of hands and feet from opposite sides, or exile from the land: that is their disgrace in this world, and a heavy punishment is theirs in the Hereafter." I think (and I could be wrong) that those who strive against "Allah and His Messenger" refers to those who do not accept Islam. In other words, this passage seems to command Muslims to commit violence against non-Muslims simply for being non-Muslims. At the very least, it puts the previous verse in a different light.