Cable of BoardMod has released a great, new template for YaBB 2.3 called Emerald Template for YaBB 2.3.  Here is a quote from Cable:

This is a dark green template that is made to work with YaBB 2.3.  Zip file includes a text file of instructions, a style sheet (.css file), and a folder of graphics.

This is based on LoneWebSurfer's Black template for YaBB 2.2.  Thanks to LWS for help with the tab menu graphics.