Palestrina is the best-known of Renaissance a cappella choral music composers. He was a prolific composer of more than 100 masses, 300 motets (which were on sacred texts but are not formalized as liturgy), many hymns, Magnificats, lamentations, and a large number of madrigals, i.e., secular music.
His popular name is derived from the name of his birthplace, Palestrina. His best known mass was the Pope Marcellus Mass. There is an apocryphal story that he wrote to the mass as the Council in Trent considered whether polyphonic music, with its secular connections and polyphonic complexity distracted its congregations and should be prohibited from the churches.
You will recall that organum often had a vigorous, throaty sound. With Palestrina, polyphony became almost suave. Whereas Palestrina was using was expressive, it was not ostentatious; to the contrary, it was sublime. While abuse of polyphony and its inclusion of secular elements were considerations of the counsel in Trent, it is doubtful that it was written for that purpose. While expressive, his sacred works are not ostentatious, but rather, sublime. Whereas dissonances were almost jarring at times in its use in organum, Palestrina used it on a weak beats or passing tones which did not jar, but rather created a bit of tension which then resolved to consonance. His style is generally considered to be the culmination of Renaissance polyphonic sacred music.
He had three distinct styles of polyphony but each shares a quality of refinement.
See http://www.britannica.com/EBchecked/topic/439795/Giovanni-Pierluigi-da-Palestrina/5470/Music for an excellent Britannica Encyclopedia article concerning Palestrina.
For examples of his middle style, and discography of its representative work, the Missa Papae Marcelli, see http://www.answers.com/topic/palestrina-missa-papae-marcelli.
For performances of the Kyrie of that work, see http://www.youtube.com/watch?v=IIcrgNtyX0U which is performed by the Tallis Singers with views of various architectural and decorative views representative of the cathedrals of that time; and http://www.youtube.com/watch?v=16cH1RZcPKs with images of the score.
For the credo of that work, see http://www.youtube.com/watch?v=A02VoJFv-jk; http://www.youtube.com/watch?v=1M8_daKHASc.
For examples of his later style, see these performances of Stabat Mater at http://www.youtube.com/watch?v=qoSQ4bYjRVs
For his lamentations, see https://www.google.com/#hl=en&sclient=psy-ab&q=Lamentations+palestrina+youtube&oq=Lamentations+palestrina+youtube&gs_l=serp.12..0i8i30.37181.37181.0.41220.127.116.11.0.0.0.376.376.3-1.1.0.les%3B..0.0…1c.1.MTFo6Tl_XT8&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&fp=2ae57bceec566c09&biw=1017&bih=444.
See http://www.youtube.com/watch?v=kcWdh6ro5Ps&feature=related for Madrigali a quattro voci.
For a performance of his Vergine bella by the Vocalia Consort see http://www.youtube.com/watch?v=wy9d5Zp3i7U