[JonnieCache]

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.

[nialo]

This is good, but not nearly as good as manually setting single character "keywords" for common searches.

[sathyabhat]

use the search enough times and you can use single character+ <tab>

[jarek]

Works well until you want to distinguish between searching en.wikipedia.org and en.wiktionary.org.

(While writing this I realized I didn't actually remember the exact domain Wikipedia and Wiktionary used... so I ran a "test" search on both.)