SharePoint 2010 brings a few new master pages that you may want to know about. There are additional master pages to accommodate both the old and new versions of UI. There are also some simplified pages to take note in.
The first master page we will talk about is v4.master. This is the default team site master page used with version 4 (obviously) of the UI. This will be the master page you typically use. It provides the ribbon bar and all of the other new visual UI changes such as the site actions menu on the left side.
If you did an upgrade to SharePoint 2010 and haven’t transitioned to the new UI yet, the old master page is still in default.master. This looks just like the master page you use in SharePoint v3 today. It doesn’t have the ribbon bar and the site actions menu is still on the right side.
The search pages by default now use minimal.master. This is a really slimmed down master page with next to nothing on it. It doesn’t even have navigation. I’m not sure why they opted to use this page in Search Center, but I think it provides and issue with people trying to leave the search center. The Office Web Applications also use this master page but that makes a little more sense because it provides more screen real estate.
The last page I will mention is simple.master. This page is used for login and error pages. From what I understand, it can’t be customized (I have no idea why), but it can be replaced.
I hope this helps if you were curious about the new master pages. I’ll also remind you again that application pages can also now make use of any branded master pages you might have created. I’ll also point out that the master pages all use properly formed XHTML although I am not sure about default.master. I will check that when I get a chance.