Was there an ancient civilization on earth at least as advanced as ours? If so, what is the best evidence for it?

At the least, I believe that the pyramid of Giza had a scientific purpose beyond being "just" a tomb, due to the chemical and structural nature of the pyramid, along with other very interesting facts about it, like its alignments. This is suggested by the underground chambers, the fact that practically no art or mummies were found inside, the broken blocks on top of the king's chamber along with the burn marks as if an explosion occurred, the types and size of stones used, the bevelling of the four sides into eight sides, the long narrow channels running out from the chambers, etc. I am not sure if this leads to the conclusion that their society was as advanced as ours or had other technology as modern as ours of which we are aware, but it is a very interesting idea.

^ I meant "or had other technology as modern as ours of which we are NOT aware. \/

Welcome back Ravosky. Back to the mysticism?

Archaeologists have admitted that even by modern standards we don't have the means to reproduce some of the ancient buildings - including the precision found in the sharp angles, perfectly carved holes that are seemingly drilled through solid rock and then, of course, we have random hot spots of radiation that are all too evident of an ancient nuclear war that is even mentioned in the Bhagavad-gita. For me, there is too much evidence that says otherwise. Unfortunately, it is extremely hard to verify when history is written by the victors. Also, considering the government's official stance on history is matched with the dating influenced by Christian mythology (A.D., B.C. Which only allows us to go back so far), we cannot depend on science that is funded by federal grants, etc..., to provide any alternative theories. The best we will ever get is to enter the field ourselves and then hope that our discoveries are accepted as truth someday. We must keep in mind, that if we were the ones currently in power - and we are also in the role of giving the final word on such things, it wouldn't make sense to admit that such a society as advanced as ours existed in the past. We wish to keep the power, not give it away to the past for scrutiny or criticism. The first place I'd look, is at the latest discoveries the military made out in the caves of Afghanistan. As for the power of having the final say, a perfect example is UFO's. Several large countries, including America's allies such as Canada's own past defense minister, has admitted the existence of intelligent life that originates from other worlds. Yet, because America hasn't said the definitive Yes as a response to the big question - it still remains in doubt. Ultimately, what America says - is. This goes for both UFO's and the past of our own world.

^Unfortunately, the few reports I've seen of the Vimanas in Afghanistan US army discovery story sound not very reliable.

Yup.