One of my new favorite websites is Contact Help. Got a dispute with your airline or need to return some defective luggage to Amazon or another retailer? Type in the website's name into the search box at Contact Help and—boom!—you have the correct phone number. The site's users regularly supplement its helpful info with updates, so check the time-stamp of the most recent comment to confirm that what you're reading is accurate.
If a company isn't in the database or you need additional help, a great Plan B is GetHuman.com, which Budget Travel has praised before as "the secret code to better customer service." The site is a cheat sheet of which buttons to press to reach a live customer service representative at a handful of companies, including dozens of travel-industry players, such as US Airways (800/428-4322, press 4, then 1).