I am amazed that so few people have ever heard of YubNub[1]. It's a service that provides this kind of feature (`g foo' to google, `gim bar' for google images, `am baz' for amazon, etc.), plus some advanced tricks (multiple parameters, default values, command combination).
!hackernews which leads to a hnsearch.com search results!
I've been using it as my default search engine for about 2/3 weeks now and its been unnoticeable (in a good way)