Given the now ubiquitous use of javascript libraries such as jquery, mootools and YUI for rich interactions across the web, design patterns are more important than ever. With numerous options of implementing functionality such as drag and drop, select a date or expanding and contracting a div, using documented design patterns make sure you don’t re-invent the wheel.

Useful design pattern references include:

• Yahoo Design Pattern Library
• Design Patterns on Flickr
• UI Pattern Library
• Pattern Tap
• UI-patterns
• Konigi
• Search design patterns
• Welie – patterns in interaction design

And for prototype tool of the moment – Axure (thanks for the recommendation Nic) – there’s a library of design and interaction patterns here and another one on Google Code here.