May I suggest the Lord of the Rings Trilogy? It’s not an allegory but it is fundamentally a Catholic work.
Tolkien: "The Lord of the Rings is of course a fundamentally religious and Catholic work; unconsciously so at first, but consciously in the revision. That is why I have not put in, or have cut out, practically all references to anything like “religion,” to cults or practices, in the imaginary world. For the religious element is absorbed into the story and the symbolism. However that is very clumsily put, and sounds more self-important than I feel. For as a matter of fact, I have consciously planned very little; and should chiefly be grateful for having been brought up (since I was eight) in a Faith that has nourished me and taught me all the little that I know."
The connection between lembas and the Eucharist is the most obvious.
“Out of the darkness of my life, so much frustrated, I put before you the one great thing to love on earth: the Blessed Sacrament … There you will find romance, glory, honour, fidelity, and the true way of all your loves on earth, and more than that…”
“I am a Christian (which can be deduced from my stories), and in fact a Roman Catholic. The latter ‘fact’ perhaps cannot be deduced.”
Just to add a few quotes from here:
The Ring is destroyed on March 25th, the Feast of the Annunciation. Imagine student audiences, unfamiliar with Catholic doctrine, being told that the Annunciation was the feast of the Incarnation, when the Word became flesh, and was therefore more important than Christmas because life begins at conception, not at birth. Imagine the student reaction when they were told that March 25th is also, according to tradition, the historical date of the Crucifixion. Clearly, Tolkien chose this particular date for the destruction of the Ring for a reason, connecting it in some way with both the Incarnation and the crucifixion.
The date of the Crucifixion per Augustine and a few others. Another quote:
If the wearing of the Ring is the act of sin, the bearing of the Ring without wearing it is choosing to bear the burden of sin without sinning. The Ring bearer is, therefore, a cross bearer. This is why Frodo Baggins is, in some subtle sense, a Christ figure. And this is why Tolkien, returning to the liturgical calendar, has Frodo leaving Rivendell at the beginning of the quest on Christmas Day and arriving at Mount Doom (Golgotha) on Good Friday. Frodo’s journey is analogous, literarily and liturgically, to the life of Christ, from His birth to His death.
A lot of people would also recommend It’s a Wonderful Life.
Vinnie