I think that the patterns and practices group has some content that will help you, though by this time you have probably found something else.
See
http://www.codeplex.com/WCFSecurity
There are some end to end scenarios in there that can help, including your database scenario.
The WCF Security guide is still in process and so parts are incomplete, but it will be released this month (may 2008).
Also, if you are using Visual Studio you can use the Web Client Software Factory to automate some of your WCF work.
http://www.codeplex.com/websf
Rob
Rob Boucher