Take a virtual trip to London with this Windows 7 theme. There's only one photo--of the London Eye from the Thames, with Big Ben on the right--but it's a nice one. The black-and-white image is dramatic, with the white London Eye set against dark gray storm clouds.
This one-wallpaper theme pack is bare bones, with Taupe windows and Microsoft's Landscape sounds--but it's definitely worth the download.
Note: To install this theme, just uncompress the zip archive and double-click the themepack file within. Windows does the rest.