Giovanni Pierluigi da Palestrina (1525-1594) was a composer during the counter-reformation and his music is the pinnacle of the classical polyphonic, contrapuntal style of sacred music. I guess even people who are fond of classical music might not be familiar with the work of Palestrina, but his music is really worth listening to, and more beautiful and more spiritual than most.
Palestrina's music can be thought of as belonging to a long tradition of (Roman) Catholic church music, but was also highly influential for the next hundreds of years. So much so that, for many contemporary Roman Catholic church goers (and clergy), Palestrina's music is still what proper church music should sound like.
For this list, I chose his Missa Pape Marcelli - which is generally considered his masterpiece, as well as being extremely important historically, linking to the Council of Trent.
Album 01: Palestrina - Missa Papae Marcelli; Missa brevis (The Tallis Scholar + Peter Philips)