Good resource on the bbc.co.uk here. It covers the definition of what is lying,;the ethical theory of lying; philosophers on lying; dificult situations like mental reservations, white lies, lying to bad people; and the medical angle - truthfulness to a patient.
There is a cultural aspect to this though. In Asia, it is somtimes considered impolite to confront, and manners would have you evade the truth. In Thailand for example, if a person fears your reaction, like you might become angry, they will give another answer. Telling the truth would upset you, so it would be rude to do so. They have a totally different take on the subject.