The multi-disc sets by the Tallis Scholars and the Hilliard Ensemble are also great introductions to Palestrina. Honestly, while I am a lover of early music, I have more music by Monteverdi, Gesualdo, Duffay, and Josquin, and nothing by Palestrina like the amount of music I have (and consider "essential") by Rachmaninoff.
From what started as a parody poll, this has turned into a great renaissance music discussion - of which there are not nearly enough!
I'll put another plug in for renaissance music. One of the top pieces in my list of essential works is Tallis' Spem in Alium. It is another one of those works that sucked me in from the first listen. Again, the Tallis Scholars have a wonderful recording of that work.
Not only would I say Rachmaninoff should be winning in this poll, but if you made a poll of greatest musicians ever, he would definitely be a candidate. That's in terms of absolute music. If you just look at Rachmaninoff on the piano, he's second to none. Sure, there's probably a few others that wrote at the same level, Chopin is one name that springs to mind, but certainly no-one better.