Companies that try to go directly head to head against Amazon (Overstock, Buy) end up meddling along unable to really gain any traction.
The ones that actually do compete with Amazon are the scrappy niche ecommerce sites. The ones that can hyper-target their marketing efforts and deliver a far superior and more engaging experience. I used to work for a company that sold specialty products and we didn't have much trouble competing with Amazon when we offered things like really detailed guides, fun product videos, unique and tailored buying advice, etc. Things that don't scale...
I think what we could eventually see more and more of when it comes to competing with Google will be niche search engines. For example, despite Google's flight search, Kayak still provides a far superior experience. Google can't effectively scale their search results the same way a hyper focused and scrappier company can.
There are a lot of verticals that could eventually begin to chip away at Google's market share moving forward. It will continue to get tougher for Google to compete in each of them.
The natural roadblock of course being initial branding to the point where people stop going to Google to find you, instead opting to go directly to your site to search (no easy task).