Google Webmaster Guidelines
A great way to learn about Design, technical, and quality guidelines..

Mobile Phone Emulator (COWEMO)
Test your website display in a variety of mobile devices

www.opuzz.com
Royalty free background music for any production

stock.xchng
Free Stock Photography - Professional and amateur photographers share over 100,000 images for personal and/or commercial use

morgueFile
Free high resolution digital stock photographs for either corporate or public use

bigfoto.com
Royalty free photo agency offering free use of all pictures

(requires link or reference)

GEek PHILOSOPHER
More free images and an extensive resource section

STOCK ICONS
Over 6300 XP Style Icons assorted in 6 Stock Icon Collections