Palestrina wrote the first requiem for Pope Gregory, (gregorian chant) thaht was written down in notation. The only recording i know of it is by the male a cappella group, Chanticleer. Only 12 voices, it is simply beautiful. I also like the requiem by the early French composer, Gilles, which has an orchestral part along with the choir. As for the rest it would be the Verdi, Berlioz, Mozart. In the same vein is Beethovens Missa Solemnis, not a requiem per se but not to be missed. Even Puccini has one, very operatic but still listenable. There is also the Te Deums of Charpentier, Vivaldi, especially good is the one by Berlioz, like his requiem, loud, stirring and like no other.