This is a sample of code to list every possible permission a user has for a particular object. The object in the code is an SPWeb, but could be a list, folder or item. As I wanted to iterate though the SPBasePermissions enumberation and display the permission names I used the code sample from here.
For a list of the SharePoint permissions see here: http://techtrainingnotes.blogspot.com/2010/01/sharepoint-permission-levels.html
There’s got to be a better way to do this… but it works.