I use a Greasemonkey script: select & hit Alt-A, searches Amazon in background tab. Alt-G, google. Alt-Y, youtube. etc.

I use Vimperator. I can search (including site-specific search keywords) or open a URL or file by hitting 'o' and starting to type.

No modifiers, no nonsense.

I love Vimperator.

Might just be a personal preference but using the address bar to search is so much more intuitive.

Couldn't you do that in Firefox with Ctrl-C, Ctrl-L, Ctrl-V? Or instead of Ctrl-L, use Ctrl-K to get to the search bar?

For Firefox: highlight text, ctrl+c, ctrl+e (to give the search box focus), ctrl-v, enter

Years of using ^C ^V have probably biased my opinion =)

I might add that for me the #1 feature that I'm really addicted to is the address bar doubling as a search bar. It just feels right.