In reply to Kemics:
It is an interesting debate. I believe, as others have said, community is the key.
On the whole it is my observation that religions with a strong missonary ethic tend to be very charitable as a recruitment drive (look how good we are come and join us etc.) this tends to cover Christianity, Islam and Judaism, but also Paganism, Sikhism, Buddhism and various Hindu sects where "good acts" generate good karma and ensure a good reincarnation in the next life. Other religions, most notably Satanism, see nothing wrong with charity but do not regard it as a major issue.
Atheists are not a community, their only common ground as a group is that they "don't" believe in something so you are less likely to get atheists forming charitable groups or even advertising that they are atheists when doing charitable work. For instance I know many atheists, including myself, who do charitable work but do not promote atheism through it. Perhaps that is because for an atheist it is an individual decision to be charitable rather than a group pressure and in this country charity has always been on the whole largely associated with religion. Even so there are many atheist charitable institutions, such as the humanist society