Frame by Frame is a blog that displays sequential images from various animated films for study and appreciation. It also shows the gif to supply reference for timing.
Frame by Frame (Blog)
Animators Resource
Animators Resource is a similar website to this one but focuses more on specific posts and videos rather than linking to other websites.
On Animation
On Animation is a website filled with animation analysis, behind the scenes, podcasts and more. Check it out!
Animator's Resource Kit 