Don't be too jealous, I'm in Mountain View and despite being a few blocks away from Google I have the same options. It's baffling.

Only SF realistically has Sonic available to them. Supposedly some backwater in Central Valley has it too.

Most people I know in Mountain View have the Comcast Business internet connection, which is basically a different company from Comcast. (Different customer service, different billing, different equipment, etc.) Apparently you can even negotiate the rate down to $75 a month, which is a lot less than I pay for Time Warner's "we are a monopoly so fuck you with a stick" package in Brooklyn.

Why does this monopoly exist? Is it related to law? Or is it related to needing a massive infrastructure to support such a business? Why can't a company "start-up" to offer fast competition in a city like Los Angeles?

In theory, they can serve most of the state: http://www.sonic.net/sales/maps/ but in practice, DSL distance limits apply. I would expect most densely populated areas of the northern SF bay counties, most especially the Santa Rosa area to be well served. OTOH, the 805(SLO) & 661(Bfd) area codes appear to be lagging.