The album "Reprise 1990 - 1999" by Vangelis is an unqualified recommendation to buy friends atmospheric music. Since I am not Vangelis expert, I can not judge whether these are really the best songs of the 90s, but they are without exception great. Especially the songs, which are backed by a choir, I like very much.
My favorites are: 13 Rachel's Song 8 Fields of Coral 7 Light and Shadow
In "Reprise 1990 - 1999" you will find beautiful, dreamy and melancholic pieces that you can listen to over and over again, without being boring.