This just happened to a friend of mine in Internet Explorer:
Help! I was changing a URL in my address bar, and before I knew it, my address bar dissappeared! I've tried everything, how do I get it back?
Microsoft posted a help page to make the address bar display again in your browser:
For my friend, she had gone to View and looked to see if Address Bar had a check mark next to it. It did. We unselected it, but nothing changed. Then we followed the Microsoft directions for the link above, and looked to the right of the browser window for a word called "Address." She found it, clicked on it, and dragged it to where she wanted the Address Bar to display. Voila.
Thanks to AskLeo.com for first posting about this.