The default behavior in Safari has always been that, while typing a URL, enter selects the most likely recommendation. Its super efficient. Why it's not the default of all browsers, I'll never know. FireFox before version 4 had the ability to auto-complete address bar suggestions. In about:config the option was called browser.urlbar.autoFill. With Version 4, that option no longer functions. As usual an extension has come to the rescue!
The enter selects add-on doesn't truly auto-fill the remainder of the the URL bar. Instead it simply selects the first suggested awesomebar result for whatever you've typed. The end result is the same. A quick "g, enter" gets me to Google, "l, enter" gets me to lifehacker, "j, enter" gets me to Jalopnik. I know I could have set up some tags on my bookmark entries, but this is a much more effective method that changes over time as the sites I visit change.
Another entry goes on my FireFox must have extension list.