I have heard the argument that nonbelievers (atheists in particular) have no morality because they do not believe that god watches over them, or something like that. (Yes, there ARE the atrocities in the Old Testament and whatnot, but that is a bit of an ad hominem tu quoque fallacy).
Are there any articles or books out there that refute this kind of argument?
Thanks in advance.
Assuming you are having this argument (or anticipate having this argument

) with Christians, why not turn to Christian writings?
I don't offhand know of any books (I don't have a copy, but "Catholicism for Dummies" - make your jokes

- is actually approved for teaching Catholicism, e.g. adults considering converting to Catholicism, and I'd assume it has something in there about this with references).
See e.g. Catechism of the Catholic Church sections 846 to 848. S. 848:
""Although in ways known to himself God can lead those who, through no fault of their own, are ignorant of the Gospel, to that faith without which it is impossible to please him, the Church still has the obligation and also the sacred right to evangelize all men.""
I am Roman Catholic, the way it was summarized to me is, there is a difference between rejecting God (very bad) vs. not believing (following your conscience). Someone who is an atheist may still be a good person, etc. A lot of this is phrased as what happens to an atheist after death (from the Catholic view, rather than the atheist view

), which is directly related to the morality of the atheist.
Some Christian denominations have a much more restrictive/exclusive view.
One thing that even many Christians/Catholics don't understand (my view, compared to the subtler distinctions I was taught) and with reference to the Catechims above is that just because you've heard of Jesus, God and the Bible and even if you've read the Bible or are otherwise familiar with Christianity, one's lack of belief is not necessarily
wilfull. It may be, maybe it even often is a deliberate rejection, but is not necessarily (a lot of Christians seem to think that unless you're living in some remote tribe in the Amazon, you can't be innocently ignorant of the Gospel).
As I recall I've read that (not surprisingly) a number of religious child abuse victims have become atheist or agnostic (I don't know if there's been any survey of percentages, this is anecdotal from news stories). Their disbelief/doubting is I think not "willful", but based upon the evil behaviour of others (or, it may in some cases be willful, i.e. a deliberate rejection of God based on what was done to them, which would be a problem).
The site:
http://www.religioustolerance.org/rcc_salv.htm
has some reference to Roman Catholic documents, I'd add
http://www.vatican.va/archive/hist_.../vat-ii_cons_19651207_gaudium-et-spes_en.html
"Gaudium et spes" from Vatican II (a very important statement) discusses atheism, and I think this section as well as others may be apropos to your arguments:
"While rejecting atheism, root and branch,
the Church sincerely professes that all men, believers and unbelievers alike, ought to work for the rightful betterment of this world in which all alike live; such an ideal cannot be realized, however, apart from sincere and prudent dialogue. Hence the Church protests against the distinction which some state authorities make between believers and unbelievers, with prejudice to the fundamental rights of the human person. The Church calls for the active liberty of believers to build up in this world God's temple too. She courteously invites atheists to examine the Gospel of Christ with an open mind." [emphasis added]