Go to Top Sites and click in the search field in the lower right of the window. Then type, for instance, wallpaper duel. You'll get a cover flow view of any page in your entire browsing history that includes those words; click on a preview to go to the site.

The Bookmarks window keeps track of more than just the places you've bookmarked: It tracks your entire browsing history. To search for Wilde's immortal words from the Bookmark window, Choose Bookmarks -> Show All Bookmarks (or press Command-Option-B, or click on the book icon in the Bookmarks bar). In the Bookmarks window, click on History in the sidebar (it's the first entry under "Collections"), and then type wallpaper duel in the search field in the upper right of the window. Go to a found page by clicking on its preview in the cover flow area; or, in the list area, double-click on it or select it and press the spacebar.

Bonus tip: You can control how much history Safari remembers for you--whether you want it to remember only a day's worth, or a year's worth, of sites (or everything until you manually erase the history). Choose Safari -> Preferences, and in the General pane, set your history length in the Remove History Items menu.