Google Blog Search

From Bloggerhacks

Google Blog Search uses Google's search technology but applies it only to blogs. When searching with Google Blog Search, results include all blogs, not just those published through Blogger.

Although you can use Google Blog Search directly, an interface to search also appears in the Blogger NavBar, allowing you to quickly search within a specific blog, or all blogs, when browsing blogs which have maintained the Blogger NavBar in the Blogger template.

Blogger Help contains a separate section for frequently asked questions regarding Blog Search.