In our web applications, we seperate our Data Access Layers out into their own projects.
This creates some problems related to settings.
Because the DAL will eventually need to be consumed from perhaps more than one application, web.config does not seem like a good place to keep the connection strings and some of the other DAL-related settings.
To solve this, on some of our recent projects we introduced a third project just for settings. We put the setting in a system of .Setting files... With a simple wrapper, the ability to have different settings for various enviroments (Dev, QA, Staging, Production, etc) was easy to achieve.
The only problem there is that the settings project (including the .Settings class) compiles into an assembly, so you can't change it without doing a build/deployment, and some of our customers want to be able to configure their projects without Visual Studio.
So, is there a best practice for this? I have that sense that I'm reinventing the wheel.
Some solutions such as storing settings in a fixed directory on the server in, say, our own XML format occurred to us. But again, I would rather avoid having to re-create encryption for sensitive values and so on. And I would rather keep the solution self-contained if possible.
EDIT: The original question did not contain the really penetrating reason that we can't (I think) use web.config ... That puts a few (very good) answers out of context, my bad.
Split it up. Use the fixed-XML storage file solution for the database connection, encrypted with .NET's built-in encryptor functions (do not roll your own). Then, using the resultant database connection, look up your 'settings table' in the database. This way you can modify your settings without a redeploy. If your customers need to be able to change the database connection string without visual studio, just write a small Windows Forms app that is capable of generating the encrypted connection string and saving the fixed-XML storage file, and, if necessary, also can connect to DB (via that same file) and modify the Settings table as the user needs.