This is a nice cheat sheet from http://outsourceage.com/wordpress3CheetSheet.html It summerises all the functions used in wordpress 3.0. It is very helpful upgrade your older themes to wordpress 3.0 compatable. The original cheat sheet is in html format.
Download WordPress 3.0 Cheet Sheet
A Colorfull version with more categories will be found here as image and as pdf . This is provided by http://academiaphp.com/2010/wordpress3-cheat-sheet/. These cheat sheet are really helpfull for a wordpress programmer and those who try to learn wordpress 3.0
wordpress is very useful and helpful.