I've been working on an opensource realmlist changer which also supports logging in to the users account and character (all optional) when launching wow. It's written in C# using the WinForms interface and requires the .NET 4.0 framework (this all means it's Windows only).
The account password is encrypted into an XML file in your AppData folder and is only decrypted on the application launch. As you can see in the source on GitHub, I am not saving any information at all. Keep in mind using the auto login functionality is optional!