Is it a religion or not? I would argue that it is not. The main reason being is that, I feel, one way to determine if a certain beleif system can be called a religion is if, within the main doctrine itself, it makes the claim to ultimate truth that this ultimate truth can only be revealed through a deity. Such a claim is not made within the doctrine of Buddhism. The doctrine of Buddhism is concerned with suffering and how to end it for one's self (sidenote: what is also interesting about Buddhism is the notion of the non-self). The guide lines to achieving this are quite simple and logical since the doctrine argues that one should not desire since desire is what causes suffering (obviously I paraphrased quite a bit). The guidlines make no mention of a diety nor of a stipulation that one should not consult a deity, in fact, many Buddhists to concult various deities. Anyone agree, disagree? Feels my definitionf of religion is way off:p?

sidenote: This does not mean it is impossible to twist this beleif system into a justification for war and violence. Siamese (modern Day Thailand) Kings often envoked the notion of "merit" as justification to conquer other lands.