Interface Trend: Modal Windows

Modal windows are perfect for login processes because they don't take the user out of context, and allow them to log in and go right back to what they were currently doing. Usually you click an "X" or "Close" button to get out of them, or click anywhere on the screen other than the window. Most of the time the screen behind the window darkens or fades out and its functionality becomes inactive.

Here are a few nice examples.

Nice Modal windows: 
http://www.nick.com/  (click "log in" or "register")
http://getsatisfaction.com/  (click "log in")
http://listen.grooveshark.com/  (click "log in")
http://www.scrapblog.com  (click "feedback" on the left)
http://www.scrapblog.com/builder/#
http://fancybox.net/example
http://www.shadowbox-js.com/index.html (scroll down for examples)
http://www.twine.com/ (fades out the background nicely)

Open/close effect examples:
http://www.likno.com/jquery-modal-windows/examples.php
http://www.ericmmartin.com/projects/simplemodal-demos/

For video too:
http://www.burconsult.com/tutorials/fancyplayer/index.html