To clarify questions that some readers might have, I do believe in salvation by grace alone, but this is equivocation if understood in the way the Reformers viewed grace. Grace for Catholics is God's unmerited help or gift, it is like a movement or energy or work of the Holy Spirit in the soul of the individual. So grace is like the life of the soul and so Salvation is by grace alone.
Faith in Catholicism is not understood as the Reformers taught. Protestantism says that saving faith is fiducia, more accurately in English: trust. In Catholicism, faith is the assent of the will to the divine revelation of God. So at my Baptist baptism I had to say that I had a personal faith/trust in Jesus, but in my Roman Catholic Confirmation I had to say "I believe and profess all that the the Catholic Church believes, teaches, and proclaims to be revealed of God". Both are statements of faith, but very different.
This becomes relevant when you look at a verse like:
"Abraham believed God and it was creditted to him as righteousness"
Was Abraham justified because he trusted in God's character, or because he believed the promises of God to make him into a great nation.
The book I really want to read on this issue is Hans Urs Von Balthasar's "The Theology of Karl Barth" where he defends the Catholic view of Grace.