United States Catholic Catechism for Adults:
http://ccc.usccb.org/flipbooks/uscca/#208
USCCB: http://www.usccb.org/prayer-and-worship/sacraments-and-sacramentals/baptism/index.cfm
Catholic Answers: http://www.catholic.com/tracts/the-necessity-of-baptism
Fr. Robert Barron: http://www.wordonfire.org/resources/video/the-sacrament-of-baptism/276/