This is a good topic to discuss. MS SQL has made granular roles for specific tasks for each user, this is for security purposes of the Database Server.
You surely want certain database owner just to be able to access their database and nothing else. Or just allow them to do a backup of their own server, this is where the database or server level roles come in.
I'm familiar of some of the roles but not all of them and at times I also forget, which role overrides the other roles, or which role is not needed.
Microsoft has the list on their site on their server level role: http://msdn.microsoft.com/en-us/library/ms188659(v=sql.105).aspx
This looks an okay reference on which is the role needed and which is not.
There is also the database level role: http://msdn.microsoft.com/en-us/library/ms189121(v=sql.105).aspx
A little off topic, I found a great blog on MS SQL versions, the list is pretty good and you will also know which version you are using. Here is the link: http://sqlserverbuilds.blogspot.com/
