The references used to back this up are to other parts of the Bible. I have always wondered about the fact that there is not a commandment that directly prohibits lying. Of course there are a few occasions when lying may appear to be the lesser of two evils. But surely the decision of when these times occur is a slippery slope.
Here's one that happened to me recently that doesn't even involve life or death: I was asked a direct question by someone, which, had I answered it truthfully, would have ruined a surprise party that I knew was being planned for her. The party turned out to be a complete success. (Except for the lying part.)
Another one that often comes up on this website is whether it is OK to lie about one's political opponent. This is usually justified on the basis that the opponent represents the essence of evil, so lying and spreading poorly-justified rumors about them is fair game.
Of course one source of impetus for the spreading of possibly false rumors is that other people don't sufficiently appreciate the "evilness" in your opponent so the evilness needs to be boosted a little.
On the other hand someone who does have a strong sense of the evil in another person will tend to believe all the rumors about them.
Of course if someone really is evil, then it will only be necessary to tell the exact truth about them to describe their evilness.
Another one that often comes up on this website is whether it is OK to lie about one's political opponent. This is usually justified on the basis that the opponent represents the essence of evil, so lying and spreading poorly-justified rumors about them is fair game.
is really quite simple. Lying about one's political opponents is wicked. Even Barak Hussein 0bama is entitled to such good name as he has. Lying about even him is wrong. For one, it violates the commandment. For another, it damages the credibility of the liar. The truth about 0bama is damning. And if it weren't (if he weren't the moral leper that he is), then the lie would be damaging a good man's good name.
IV. RESPECT FOR THE TRUTH
2488 The right to the communication of the truth is not unconditional. Everyone must conform his life to the Gospel precept of fraternal love. This requires us in concrete situations to judge whether or not it is appropriate to reveal the truth to someone who asks for it.
2489 Charity and respect for the truth should dictate the response to every request for information or communication. The good and safety of others, respect for privacy, and the common good are sufficient reasons for being silent about what ought not be known or for making use of a discreet language. The duty to avoid scandal often commands strict discretion. No one is bound to reveal the truth to someone who does not have the right to know it.283
2490 The secret of the sacrament of reconciliation is sacred, and cannot be violated under any pretext. "The sacramental seal is inviolable; therefore, it is a crime for a confessor in any way to betray a penitent by word or in any other manner or for any reason."284
2491 Professional secrets - for example, those of political office holders, soldiers, physicians, and lawyers - or confidential information given under the seal of secrecy must be kept, save in exceptional cases where keeping the secret is bound to cause very grave harm to the one who confided it, to the one who received it or to a third party, and where the very grave harm can be avoided only by divulging the truth. Even if not confided under the seal of secrecy, private information prejudicial to another is not to be divulged without a grave and proportionate reason.
2492 Everyone should observe an appropriate reserve concerning persons' private lives. Those in charge of communications should maintain a fair balance between the requirements of the common good and respect for individual rights. Interference by the media in the private lives of persons engaged in political or public activity is to be condemned to the extent that it infringes upon their privacy and freedom.
The saints wouldn't tell a lie to save the world.
Here's a good article about sticky situations where concealing some truth may be necessary but lying not: