The Saint-Saens Requiem should be far more well known. It is such a great piece of music and doesn't outstay its welcome unlike the Verdi, Berlioz, Dvorak and others imo. It is a crucial link between the grand rather operatic Requiem of Berlioz and the inwards felt and consoling Requiem by Saint-Saens favourite pupil Faure. Therefore it holds a very important position in French sacred music.
My favourite highlights, although the whole Requiem is great:
Requiem-Kyrie: Great start with a string figure somewhat reminiscent of Mozarts Requiem. It sounds like the strings are crying. Great vocal build-up for the soloists and the choir. More in the tradition of Berlioz and Mozart. Stunningly orchestrated.
Dies Irae: This is a Dies Irae which sounds as imposing as the Berlioz or Verdi Dies Irae. Great climax for Organ and orchestra
Oro supplex: Once again great string moments and incredibly poignant singing here with a celestial finish.
Hostias and Benedictus: Beautiful consoling music which seems to foreshadow Faure quite a bit. Here i think is the turning point of French Requiem music to something much more gentle.
Agnus Dei: This is easily the greatest part of the whole work. Probably one of the greatest Agnus Dei ever written. The climax is gorgeous.
There is a doctoral thesis about the S-S Requiem out there which can be read via Internet and which illuminates these points further i think.
The best recording imo is by the London Symphony and Geoffrey Simon.
Other favourites are of course Faure, Durufle and Mozart. But also Schnittke, Takemitsus Requiem for Strings (does it count??) and the short but beautiful Puccini Requiem.