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.
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