Sites with great user logins, or great UI in general?

This is more of a design showcase site, but you can have a look at Behance and you might find some inspiration. You can also filter by web design, web development, UI, information architecture, or interaction design:

http://www.behance.net/?sort=appreciations&time=all&...

State farm actually has a really setup for login. It's in the right place (should always be upper right), and its obvious but not obtrusive. It expands to show the password field when you click it. http://www.statefarm.com/

Have you checked dribbble?

http://dribbble.com/search?q=login