- Connection Manager (XMLHttpRequest / AJAX)
- DOM (manipulating the elements (style, coordinates) in a loaded web page)
- Drag and Drop
- Event (adding them to existing elements on a page)
Yahoo! Design Pattern Library is a set of solutions to common problems (breadcrumbs, autocomplete, drag/drop, pagination etc). There is no code, but it does demonstrate the solutions Yahoo uses for its sites.
They also have a blog about it: Yahoo! User Interface Blog.