Most Important Catholic Author for Today
It's somewhat hard not to say Chesterton, but I really think it's Pascal. You can download his Pensees or "Thoughts" here in a number of formats including a nice PDF. Kreeft also has a nice book which has the text of Pascal interspersed with his own notes.
One really nice feature of this work is that it consists in proverb-sized aphorisms which can be digested in small chunks.