I've have these banked for a while, mainly because they help the utterly clueless when it comes to layouts and styles:

For total newbies:
zvi's explanation of styles.

unboxed gives an image-based description of how to change to a customized style.

For creating themes and/or layouts: Resolution/Browser Data for DW users

starlit's Tutorial on Adding LJ Layouts to DW

Quick and Dirty Guide to Creating a Color Scheme

User input on what's important in a layout at visualwit.