Do Buddhism and Atheism contradict each other? Can a person be an atheist and a Buddhist at the same time? Or are some beliefs in deities too important to the practice of Buddhism?
Within the canonical texts of the various schools of Buddhism there are various beings that roughly correspond to that of deities, in particular Devas and Brahmas. Both Devas and Brahmas are particular types of beings who have taken very high rebirths as a result of their good Karma. They have very long lifespans and many wonderful benefits.

However they aren't the objects of reverence that they are in other religions. Although one might pray to or request one of these beings for help in worldly matters it is understood that these beings are rather limited, and they eventually die like any other being.

In practical terms rejecting the existence of such beings doesn't really present major problems as it isn't an essential doctrinal teaching. One can be a practicing Buddhist without believing in them.