We need an elegant weapon for a more civilized age. Actually, I suggest two.
Safari's Develop Menu
The first step is to enable Safari's Develop menu. To do that, go to Safari's preferences, click on "Advanced" and check the box next to "Show Develop menu in menu bar." (Note that an earlier version of this article suggested doing this via the command line using "defaults write com.apple.Safari IncludeDevelopMenu 1," which will work but is obviously not as easy.)
The Develop menu includes several handy little features, including the ability to open the current page in another browser, or change the User Agent that Safari sends (which can be handy if you want to see the iPad or iPhone version of a page).
Create a custom keyboard shortcut
To create that shortcut, go to System Preferences » Keyboard » Keyboard Shortcuts.
Select "Application Shortcuts" from the left column, and then click the "+" sign under the second column. You can see mine here.
Notice that I have made several shortcuts for Safari, yours may look differently than mine. That is completely OK. The important thing is to make sure that you're in the right place: Application Shortcuts, and then press the "+" key.
That will bring up a pop-up window. Choose "Safari" as the "Application" and in the "Menu Title" field type:
You must get the spelling and capitalization exactly correct. I recommend using copy/paste of that line above.
Then choose whatever Keyboard Shortcut you want. (I chose command (⌘) + shift + J because ⌘ + J is used for Edit » Find » Jump to Selection.) Your new shortcut should look like this:
Click "Add" and switch back to Safari. In recent versions of OS X, shortcuts are immediately updated, even if the app is already running. In older versions you had to restart the app to see the shortcut.