The Open Directory Project is an amazing  resource. According to Wikipedia: "The Open Directory Project (ODP), also known as dmoz (from directory.mozilla.org, its original domain name), is a multilingual open content directory of World Wide Web links owned by Netscape that is constructed and maintained by a community of volunteer editors.

Under society, the link for Religion and Spirituality contains 36 religion categories including atheism.

• Advaita Vedanta (220)
• African (166)
• Agnosticism (45)
• Atheism (223)
• Baha'ism (274)
• Buddhism (3,276)
• Cao Dai (13)
• Christianity (78,358)
• Confucianism@  (48)
• Deism (60)
• Esoteric and Occult (2,636)
• Ethical Culture (26)
• Falun Dafa (27)
• Fourth Way (123)
• Gnosticism (136)
• Hinduism (1,403)
• Humanism (112)
• Islam (1,852)

• Jainism (37)
• Judaism (2,473)
• Modern Movements (77)
• Native American (55)
• New Age (1,704)
• New Thought (116)
• Noahidism (10)
• Pagan (2,259)
• Pantheism (48)
• Scientology (634)
• Shamanism (126)
• Shintoism (17)
• Sikhism (186)
• Spiritualism (330)
• Taoism (418)
• Unitarianism and Universalism (1,168)
• Universal Life Church (21)
• Zoroastrianism (45)