Slashtag.it is an interface that lets you access several dozen search engines more quickly. You can accelerate your web search by up to 80%! It does this via simple slashtag commands -- one for each of a couple dozen different search sites.
If you wanted to search for U2, for example, across several different sites, there's no need to visit them all and type "u2" Prime into their search boxes. You can do it all via Slashtag.it, like this:
There're currently about 60 slashtags supported and a form to suggest new ones that you'd like added. Slashtag.it supports pretty much all of the main search sites and a few cool ones like Netflix, Evernote and Dropbox. (If logged in to your Dropbox account, typing "somekeyword /db" searches your stored files; too cool.)
You can make it the default search tool on your Firefox, Chrome, Internet Explorer or Opera browser; it can also be added as an extra toolbar on Safari, though it won't function as part of the main search box there.
And, Slashtag.it doesn't have to replace your primary search engine; if you use it without typing a slashtag, it'll send your search term to your preferred search engine.