And a quick Googling of the term “the next Silicon Valley” shows Seattle, Los Angeles, Bangalore, Tel Aviv and even the Brooklyn tech triangle (yes – really) have all thrown their hat into the ring thinking they could be contenders.
I am highly skeptical that LA or New York could be the next Silicon Valley because their costs of living are so high already. If you're going to pay that much for an apartment and want to do a startup, you might as well move to SV already.
Seattle's prices have been rising for years too, and, although it's much less expensive than NYC or coastal CA, building in Seattle is still difficult and expensive.
Austin, Texas is perhaps the most interesting possibility on a cost-of-living basis.
(For more on why this matters, see Yglesias, The Rent is Too Damn High: http://www.amazon.com/The-Rent-Damn-High-ebook/dp/B0078XGJXO).