I would write a more complete post on Why I am a Catholic, but I would be merely transcribing from other sites.

www.catholicapologetics.net gives an almost complete explanation on Catholicism, why we do what we do, why Our Lord did what he did, why the popes are the successors of St. Peter, the authenticity of the Bible, refuting Islam and Protestantism, and so much more.

www.newadvent.org is the 1917 Catholic Encyclopedia that contains thousands of articles like the writings of the Church Fathers, the Summa Theologica of St. Thomas Aquinas online, gives definitions of objects, positions, articles, tells lives of saints, and an incredible amount more.

www.drbo.org is the complete Douay Rheims Bible online.

God bless!