How to auto-complete url in safari

Enable web sharing and place the PAC file (e.g. proxy.pac) in the documents folder (/Library/WebServer/Documents). Then set the auto proxy setting to http://127.0.0.1/proxy.pac. If the changes don't take effect immediately or you change the contents of the PAC file at any point in time you need to restart Safari and clear its cache. If this doesn't help, reboot the system.

Safari maintains this information internally, but I've only been able to make it divulge the actual URL by enabling the web inspector (Option-Command-I) after you have enabled the Debug menu at the bottom of the advanced tab in Safari Preferences (Command-,). You can of course drag the URL out of the search window to get a link (instead of copying which just copies the visible search terms).

You will see the Full URL under the Location disclosure in the bottom right corner of your screen. The only good part of this is the text is copyable once you've navigated and selected it. It might be possible to write a Safari extension to perform this copy, but I have not found one to do this yet.

As provided by Arjan you can also make a bookmark and use JavaScript to retrieve the URL.

javascript:(function(){window.location.href=window.location.href.replace("search?", "#");})()

You might also be interested in gDirectLinks or it's more fully fledged sibling LinkThing which change the way Safari renders google search terms and works with URL handling from google.