"The question of human procreation, like every other question which touches human life, involves more than the limited aspects specific to such disciplines as biology, psychology, demography or sociology. It is the whole man and the whole mission to which he is called that must be considered: both its natural, earthly aspects and its supernatural, eternal aspects." ~Paul VI, Humanae Vitae
This is a reminder that today marks the 40th anniversary of Humanae Vitae. Celebrate by reading the encyclical or the resources noted below.
UPDATE: Sonitus Sanctus has posted links to an mp3 of Dr. Janet Smith's "Contraception, Why Not?" It is the best summation of the Church's teaching on the subject. Period. And very accessible... Also posted is a recording of a debate between Dr. Smith and Dr. (formerly Fr.) Charles Curran. Excellent and not-to-be-missed!