For years I've used a few apps that I created that let you send searches directly to Amazon, iMDB, the Python Cookbook, etc. The last app of this type I wrote is the searchexplorer sample included with PythonCard, which was a port of a Visual Basic (VB) app which I'm pretty sure was based on an even earlier HyperCard app, but I can't find the HyperCard version. The reason for such a utility is twofold: one it lets you easily find a cached search, so you can get to a page even if you are working offline, but the most important reason for me was that it saved going to the sites, finding the search box, specifying the type of search, etc.
Anyway, as of today I no longer need to use my earlier hacks. I found iSeek, which sits in the Mac OS X menubar, exactly where this type of utility belongs. iSeek comes pre-configured with setups for Amazon, iMDB, dictionary.com and most of the other sites I typically search; of course, it supports Google too, but that isn't as important since there is a Google search built-into Safari.
You can try out iSeek for free and/or watch a movie of iSeek in action. A license costs $15. Of course there is still the need for this kind of utility in the Windows task bar for the rest of the world that doesn't use Mac OS X, but I'll leave that as an exercise for the reader.
Now I just wish GameFAQs and a few other sites would support GET style search requests instead of requiring a form POST.