Tower Defense

[Gogan]

In case WoW isn't addictive enough for you, I present Tower Defense:

http://novelconcepts.co.uk/FlashElementTD/

There's another interesting variation at:

http://www.handdrawngames.com/DesktopTD/

If you play the latter, I've created a "score group" called Eventide. Just specify "Eventide" after you obtain a score and you can compare it to the rest of us.