The short version is:
You can create your own ConfigurationSection and ConfigurationSectionGroup (reference System.Configuration, first). Then, you define a in your web.config to support your custom sections.
If you want intellisense, you need to modify C:\Program Files (x86)\Microsoft Visual Studio 10.0\Xml\Schemas\DotNetConfig.xsd to include the detail of your new sections.
For example, let's say you want config that looks like this:
<tomWright.Framework>
<settings awesomeness="High" coolness="Medium"/>
</tomWright.Framework>
You'd create a ConfigurationSectionGroup called something like TomWrightFrameworkConfigurationSectionGroup (which inherits from ConfigurationSectionGroup) and have it have one property called Settings, which points to a another class SettingsConfigurationSection (which inherits from ConfigurationSection). There are a few examples on MSDN on how to do this.
It's a bit of a learning curve, but when you want to make the leap from simple appSettings, to custom configuration - there's really only one way to do it, and it's not particuarly intuitive. If you have any questions though, let me know, I've done a fair with this before. Hope that helps... -Rob