This one is just for the designers and developer who have the painful task of skinning existing widgets to make them integrate tightly with their applications (or more likely: their employer's app): ThemeRoller.
Filament Group provides a simple tool to interactively skin the existing jQuery UI widgets, and then download the newly created skin - taking a whole host of pain out of designing the skin.
The interface allows you to pre-select from existing themes, or roll your own, each time any changes are made, a live complete preview is rendered (by layering a new style sheet in the background).
So if you use jQuery UI tabs, accordion, slider, date picker or dialog box then this will be the fastest way to skin.
Perhaps the most exciting feature of this tool, is that once you've styled to your heart's content, you can download the current theme. A complete zip file will all the classes marked up with your selected colours. Perfect.
On top of this, jQuery 1.2.6 was recently released and jQuery UI 1.5 has also just been released.
The API browser is up to date with the latest documentation, and I've been working quietly behind the scenes to get offline version(s) of the API browser working...watch this space!
Congrates to the jQuery team on another great step forward.