Michael Waters and other archaeologists have published their long-rumored findings from the banks of Buttermilk Creek in central Texas. At this site there is a strong Clovis component, the earliest universally accepted human culture in the America; Clovis dates to around 13,300 years ago. At Buttermilk Creek there is another cultural horizon beneath the Clovis material, with thousands of stone artifacts and a series of OSL dates in the range of 15,000 years. This is the best candidate for a "pre-Clovis" site I know of, and it joins several others which may be as old.
If people really were in the Americas 15,000 years ago, this raises many intriguing questions. Why did their population grow so slowly that there are only a dozen or so possible sites from this period, as opposed to the thousands of Clovis finds? Why did they not have a discernible impact on the environment, in terms of extinctions and excess fires? And what about the genetic evidence suggesting that almost all Native Americans are descended from one small founder population? The idly curious should check back in about two years and see how the debate is unfolding.
UPDATE: see my further thoughts on this site here.