While I’m not a big fan of the ads and pop-ups, I find the airport guides at iFly to be very useful. With a few exceptions (including TRI, the airport closest to my parents) you can find information on almost any airport in the world. The guides typically include information on when the airport opens, security, parking (locations and rates), maps, and listings of services and amenities. There are also suggestions for activities should you chose to leave the airport during a particularly long layover.
In addition to the airport guides, the site also has links to flight trackers and a section devoted to travel advice including a special section for inexperienced flyers. More seasoned travelers can benefit from reviewing other sections on getting bumped, customs/VAT, and EU travel regulations.
Again, it’s not the most visually appealing site and the ads are a nuisance but it’s a great (free) resource for travelers.