Well, I believe that there are other sentient races and life out there somewhere, but it remains to be seen whether our race has ever been visited by them which I strongly doubt (at least in the way described in previous posts).
And actually, one thing they think could have made belief in gods and other deities stronger, was the accidental finding of extinct prehistoric creatures. In more obscure records of ancient writers and historians, there are numerous accounts of ancient Greek villagers on this one island that kept plowing up strange animal bones that paleontologists recognize as extinct creatures from the Pleistocene era. Of course the people 2000 years ago would not have recognized them as such, and would have considered them to be the bones of heroes and creatures of myth.
Also there's a theory that the griffin (sp?) of ancient mythology was actually the fossilized remains of a protoceratops (sp?) which the Scythians, steppe nomadic tribes, were showing travelers passing through the area during the 6th century BC and maybe even earlier. Though these fossil remains may not have created many of the ancient culture's myths and gods and legends, it very well may have given people back then proof of sorts as to their existence.
And as far fetched as this may seem to some people, it's actually quite plausible given that many ancient civilizations carried out construction work for roads, wells, and cisterns; as well as mining for resources which could have put them in further contact with millions of years old fossil remains.
Just some more food for thought. Not that i'm trying to be purposely rude and argumentative, it's just something that i'm very passionate about as you may or may not see in my posts regarding said subject. But then again amazing discoveries are found alot in the fields of archaeology and paleontology and who knows what may be found somewhere down the road?