Drupal ships with a user login block, but it's a little heavy for a lot of projects I work on. It includes the login form itself, and that's kind of a pain to style and might not have been considered in the initial design phase of the project. What I often need is just a more simple "Hello [user], Logout" link, or - in the case that user hasn't logged in yet, a simple "Login or Create Account" link.
You might think that you could just drop some links for this into the theme, and you can - but there's still some PHP logic to see if the user is logged in or not. Not a big deal, but it's a pain to have to do that over and over for every drupal site I build. So, here's a little module I developed which just outputs a block for these links.
Note: This module has been updated and improved with added tools to configure the links, and support for Token (thank you Chewits).. you can now find it here: