When I went to a Sarah MacLauchlan's concert in Hammersmith in 2005, she said "My manager insisted I sing this one. He said this would be the only song people knew here!" and she laughed. What a modest + lovely woman.
Sarah herself has produced dozens of amazing songs, but "Silence" by Delerium is absolutely outstanding.
Beside the original version, I like Delerium's own "Sanctuary Mix" which is included in the bonus CD of "Karma". DJ Tiesto's "in Search of Sunrise Remix" is included in Sarah's CD 'Remixed', but I personally prefer the intense/edgy feel of 'Sanctuary Mix' by Delerium themselves. I am not sure but this version seems to be included in CD 2, not this one.