Jim just asked me about what I used to do a quick Wikipedia search in Safari - I just hit a key combo and a text entry window pops up, where I entered "w trans lux" and got to the wikipedia page for the company behind the awesome Mighty Hercules cartoon.
I'm using Shortwave to search all kinds of crap - it's like the Firefox search shortcut dealie, except that you don't have to inflict Firefox on yourself in order to use it. It's just a javascript bookmarklet that is configured to search a bunch of services, and you can extend it with your own services by editing a text file. I have it set to search my own flickr account for stuff, search my blog, my delicious.com account, etc... Very cool.
And if I put the bookmarklet on my bookmarks bar, it can be triggered by a keyboard shortcut - on mine, it's the 9th bookmark in the bookmarks bar, so ⌘+9 brings up the box, and I'm off and running.
Easy. Free. Extensible. Shiny. Now you know, and knowing's half the battle.