Living where we do, we're pretty much in the clutches of Delta, so I don't spend much time at sites like Expedia.

However, I have a friend living in France who would like to be able to compare prices for flights. Since most of her trips would be from Paris to New York, she should have lots of airlines to choose from.

What would be good sites for her to look at? Preferably sites through which she could actually book flights.