* Styled select boxes
* Good cross platform datepicker with ranges that looks good
* More form validation options / dynamic form validation
* A good drag api that does edge detection well in every browser
* Bring back frames (would allow good nested routing)
* A built in rich text editor
* A good modal API (or bring it back)
* A way to submit a form via AJAX with just a property (think Rails UJS) to just render html.