Squat Captcha - The worst captcha ever! Forces you to do 10 squats
Interfacer - Collection of more than 200+ free design resources
Humans Not Invited - CAPTCHA that filters out humans and only lets programs pass
Facebook Design Resources - A collection of free resources made by designers at Facebook
reCAPTCHA - reCAPTCHA is a free security service that protects your websites from spam and abuse.
Freebiesbug - Collection of the best free web design resources.