However there are still lots of people using Prototype or at least would be willing to use it with UI libraries by Scriptaculous and do some awesome stuff. In some level I still prefer Prototype and Scriptaculous to JQuery. Jarvis Badgley has summed this issue very good in his blog post.
If you are stuck with Prototype and Scriptaculous, there are still great and working plugins that extend Prototype and Scriptaculous. I will list now three plugins that I have lately found helpful.
Carousel is a highly configurable Prototype extension that creates a nice way of presenting content that is logically broken into several pieces / steps / etc
Accordion by Kevin Miller is a lightweight accordion that supports both vertical and horizontal accordions.
Do you use still Prototype and Scriptaculous? Have you any hints or recommendations about great plugins?