You probably know that there is an application called Keychain Access on your Mac OSX system. But did you know that you can reveal all the passwords stored in it? Keychain Access stores all kinds of passwords, such as Wi-Fi networks, ftp access, websites, mail, etc.
For example if you have a bookmark in Transmit with a password stored in it and you want to retrieve it you can go to Keychain Access search for the name of the server you are interested in. Select the right key and get info with Apple(Cmd)-I. Now you will need to click the Show password switch which will prompt you for your admin password. Once you typed it in, the password for that specific key will now be visible.