Boxes and Arrows discusses defacto design standards on the web.

Design elements used by more than 70% of the sites studied included:

• A logo in the upper left corner linking back to 'home'
• Global search equating to a text field and button
• Top or horizontal placement of top-level categories
• Text rendered as a graphic for top-level links
• A cart metaphor for the View Cart function

Less common on sites were breadcrumbs (45%) and underlined links (62%).