My favourite is the domain tab completion automatic site search recognition thing. Chrome users know what I'm talking about. It's fantastic.

EDIT: https://sites.google.com/a/chromium.org/dev/tab-to-search

Basically I can type the first few characters of a domain until it autocompletes, then hit tab, then enter a search term which is submitted to that site's own search form, which chrome picked up when I went to the site, using various heuristics.