This is a question more than an answer.
Could either the Roman Stoics or the Pythagoreans be considered atheistic religions?
Buddhism is only atheistic in the sense of there being no creator God.
The Buddha described many realms of non-material existence and called the beings who lived there gods. The lowest heavenly realm is the home of fairies, elves, trolls, nagas (shape shifting reptalians), Sasquatch (Yakkhas), and many more. The highest realm is the realm of Neither-perception-nor-non-perception, where beings have no form or way of communicating. There are a lot of higher realms in between.
Although there's no creator God in Buddhism, there are beings who believe they created the universe and have followers among the gods who believe that.
Interestingly, you can take any deity from any religion and find a place for it in Buddhist cosmology. The Buddha didn't teach that other peoples gods didn't exist, he taught that they are not free from death and the round of rebirth. This is why most Buddhists don't worship any gods (some do, for some reason).
http://www.accesstoinsight.org/ptf/dhamma/sagga/loka.html
http://www.accesstoinsight.org/tipitaka/dn/dn.11.0.than.html#bigbrahma