Chrome: While you can always make your own custom search keywords, you have to manually make them for every site you search. The Omibox Site Search extension saves you the trouble by just searching the domain you're currently on.
Omnibox Site Search is essentially a search keyword for any site you want — so instead of searching a domain using the site: operator (e.g. site:lifehacker.com.au searchterms), you can just type s on your keyboard, enter your search terms, and Chrome will search whatever site you're currently visiting. It's perfect for those sites you don't search as often, or if you're just sick of creating shortcuts for every ding-dong site you need to search (and on every computer you own, since Chrome still doesn't sync custom search engines). Certain sites, like IMDB, The Pirate Bay, YouTube and more will even search using their own engine instead of Google. Check out the extension for more info.
Omnibox Site Search is a free download, works wherever Google Chrome does.