Lea Verou has, rather masterfully, created a large library of CSS animations here: http://leaverou.github.com/animatable/
While this is undoubtedly an excellent way of showing off the capabilities of CSS I would still strongly advise against simply rushing out and plugging as many as possible into any site you may be working on.
Libraries like this tend to make us all think of ways to show off our prowess as developers by employing as many of the latest, cutting-edge techniques as possible. However, this isn’t necessarily good for the site or it’s users.
As UX designers and developers we have a responsibility to both the product and the user – we need to make sure that those to things fit together as neatly as possible – A few flashy animations may look fantastic when you first arrive at the site but how are they after you’ve had to live with them for 10 minutes while you’re using the site? A lot of these animation can quickly become annoying or even obstructive when you’re trying to achieve something.
On the other hand, some browsers are not capable of rendering fantastic new CSS properties or animations. We need to be sure that processes in our site don’t rely on anything that might not be available to all our users. We also need to make sure that nothing is lost from the message of our product if the CSS fails because the browser can’t render it.
I guess the overarching message here is that CSS libraries are great for ideas but we should not lose sight of what is important to our product or our users.