A while back I blogged about how you could use the SPSecurityTrimmedControl to manage the display of content based on user permissions. The PermissionsString is where you specify what permissions the user must have to display the content. Until now I wasn't sure what values you could use, and the SDK although much imporoved wasn't exactly forthcoming. While using a reflector I managed to track down the SPBasePermissions enum which reveals all the possible values.
And here they are grouped in the same way you would find them in the SharePoint permissions list:
List Permissions
Site Permissions
EnumeratePermissions
Personal Permissions
And an example of usage if you are reading this and haven't seen the control in action before:
<SharePoint:SPSecurityTrimmedControl PermissionsString="AddAndCustomizePages, ManageLists" runat="server">
<%-- some content here ... %>
</SharePoint:SPSecurityTrimmedControl>