MrTunnel.com
Discusses many projects.

The Tunnel Page
The longest road and rail tunnels in the world, grouped by categories such as sub-sea tunnels and immersed tubes.

Bridge of the Month Quiz
An image is posted inviting entrants to identify the feature. A free copy of a book on the subject is awarded to one correct entrant per month.

The Bridges Project
Online database of significant bridges compiled by the Department of Civil Engineering at Rice University. Includes photographs.

The West Point Bridge Design Contest
Annual competition sponsored by the American Society of Civil Engineers. Includes free software download.

Structurae: International Database and Gallery of Structures
Compilation of many features worldwide, including bridges and tunnels. Some entries include photographs.