Adding a few more resources I've come across to the many already great suggestions above:

1) Pattern libraries:

• UI Pattern Factory: http://uipatternfactory.com/
• Nokia Mobile Design Patterns: http://wiki.forum.nokia.com/index.php

2) Other related resources, blog posts, anti-patterns:

• Patterns to avoid for iPhone developers (antipatterns): http://vator.tv/news/show/2009-04-02-patterns-to-avoid-for-iphone-developers
• iPhone Application UI Design Patterns (blog post): http://flyosity.com/application-design/iphone-application-design-patterns.php
• Designing Social Interfaces: 5 steps, 5 principles, 5 anti-patterns (slideshare presentation): http://www.slideshare.net/emalone/designing-social-interfaces-5-steps-5-principles-5-antipatterns-2014474
• Typographic Design Patterns and Best Practices: http://www.smashingmagazine.com/2009/08/20/typographic-design-survey-best-practices-from-the-best-blogs/

Resources i've used in the past are:

• Welie.com - Interaction design patterns
• Yahoo! Design patterns

Matt

To add a few:

• ecommr: ecommerce examples
• Designing social interfaces

The UX Pattern Explorer by Infragistics Quince is great: http://quince.infragistics.com/

I have recently started my blog of safety-related HCI patterns for touch-based applications at patterns.intuio.at, a rather specialised collection of patterns.

Echoing earlier posts: +1 to Yahoo! Design Patterns and +1 to UI Patterns

Both are very useful, in comparison to Quince. The Yahoo! pattern library sets a nice standard that I enjoy referring back to as a resource. The Quince interface is a bit over the top to be something I would want to use regularly.