we learn from sarah that in a situation where you can get a person very angry (which is equated to idolatry) it is OK to lie to them. in what other situations is it OK to lie to a person?
When there is a serious risk of causing bad relations between people if the lie is not told.
See K'subos 17. This is learned from the acceptability of praising an apparently unpraiseworthy bride on her wedding day. I have vastly oversimplified the issue, but the point the G'mara is making - as evidenced by Beis Shamai's objection to Beis Hillel, which shows that Beis Hillel was really suggesting lying and not just evading the question - is that we have lower standards for distancing oneself from falsehood when there is a great danger involved (even non-capital danger).