I'm looking for a way to list all pages where a given user is an administrator. Is this possible? If so, where should I be looking?

Not sure what you are looking to accomplish. If you want to prompt the user to add your app to a page the are an admin of, you can do it through the javascript SDK. (https://developers.facebook.com/docs/reference/dialogs/add_to_page/)

Otherwise, you need to use FQL to query for the information. (https://developers.facebook.com/docs/reference/fql/page_admin/)

You'll need the manage_pages permission from your user in order to gain access to this information.

Using Facebooks FQL and the Graph API you can make a query to the page_admin table using the uid index to reference your user.

https://graph.facebook.com/me/fql?q=SELECT page_id, type from page_admin WHERE uid=me()

An alternative :

The /me/accounts Graph API endpoint
In the Graph API's documentation under the user endpoint there is details about the accounts connection :

The Facebook apps and pages owned by the current user.

You also need the manage_pages permission from your user here.

Here is a sample output from a call to that endpoint :

https://graph.facebook.com/me/accounts?access_token=ABC

...
    {
      "name": "Unicorn Ville", 
      "access_token": "XXX", 
      "category": "Application", 
      "id": "123"
    }, 
    {
      "name": "StackOverflow'em Poker", 
      "access_token": "YYY", 
      "category": "Application", 
      "id": "456"
    }, 
    {
      "name": "The Official Bausley Page", 
      "access_token": "zzz", 
      "category": "Non-profit organization", 
      "id": "789"
    }, 
...

Note that /me/accounts returns "apps and pages owned by the current user"; As such the results you will get will have to be filtered, removing all the application entries or alternatively extracting only the non "application" values of the category parameter.