Noty allows you to add simple notification "popups" that you see in many modern applications, like twitter, Facebook, iPhone etc

It's free and can work in many different ways depending on the user experience you are trying to create.

http://needim.github.com/noty/?utm_source=javascriptweekly&utm_medium=email

This link includes the code, but also a "Run It" open so you can try it out with no coding.