Okay, I guess this is something that many of you have already heard/read somewhere, but I thought it would be nice to bring it up for those who haven't

FROM IOLKOS TO THE ATLANTIC: Another unconventional and more revolutionary theory which really deserves particular mention is that of Henriette Mertz, an American archaeologist and researcher of the Hellenic Prehistory.
After 1950 Henriette Mertz, following Apollonius Rhodius' scripts on Argonautica Book II, sailed over the east coasts of S.America and across the Amazon, covered long distances on foot in the Andes range in Peru, Bolibia and Colombia and then she came to the conclusion that the Argonauts had sailed as far as South America where gold was in plenty. According to her, the Miletian geographers quite mistakenly placed Colchis in the Euxinus Pontus where the ancient philologists sent off the Argonauts to get the "Golden Fleece".

"Apollonius Rhodius accurately described the high tide surging through the passage and the white-foamed spray clashing high on cliffs of both sides - the Cyanean Rocks. The allusion of rocks clashing together referred to the high tide - as the tide swelled rushing in, lower rocks became submerged by the rising seas, disappearing from sight and appearing to widen the passageway giving an optical illusion of the two headlands moving away. When the tide receded and the water level dropped, lower rocks again became exposed and appeared to suddenly come together. Thus they opened and closed. Since the vast surge of foaming sea rises twice every day with an unexpected suddenness the rocks were said to clash together (Symplygades-Clashing Rocks)".
According to Mertz the detailed and accurate description of this natural phenomenon would be possible only by eyewitness and this phenomenon exists precisely as described and exists in no other place.

Source
Apollonius Rhodius' Argonautica in English

Very interesting. And not surprising either. Whether it's Romans in Texas, Celts in New Hampshire, or Phoenicians in Massachussetts it seems every ancient culture has visited the Americas' long before Columbus..

now, i belive the celts and phoenicens, but could you elaborate on the romans in texas?

I remember reading an article in an Archeological periodical a ways back that said there had been stashes of Roman coins,weapons and armor found along the Texas coast. I can't vouch for the truth of that but given how many other cultures have been here it seems likely enough..

There is also a theory that the Africans were in Latin America prior to AD.

I agree that it would be of no suprise if any of these ancient civilizations visited the Americas prior to Columbus. The more we investigate the more we learn.

It seems that it's easy for us to forget (living in our technologically imposed lack of daredevilesness) that in ancient times people were much more bold and willing to take risks and chances. For us seems a folly to cross the Atlantic (let alone the Pacific) with small "wooden boats". Actually, those ancient mariners, were really skilled and able navigators, well able to perform such trips
And not on "wooden boats", but on well-manufactured vessels that could take the hostile ocean conditions

Asterix, I agree with the majority of your statement, but I think that we are just as bold (if not more so), but without the means to continue our exploration on the scale we did during those times. Our "new world" is in the heavens and to explore these areas it requires more expensive resources which are not as plentiful or inexpensive as say wood and metal were. Of course let us not forget the science behind it or the time it takes to successfully launch one craft. But there is one resource we are plentiful in: bold, curious, and willing participants.

Quite right, and I guess the other difference is the...technicalities in our time that were either non-existent or much less present in ancient times.
For example, think of all the funds/voting/decision NASa has to go thru before launching a probe