Interaction Design Patterns

http://www.welie.com/patterns/
= must have
Online Resource
FREE

Martijn van Welie has put together a very valuable and useful collection of interaction design patterns, which can greatly help the work of interface designers and information architects working at Web or other general electronic interface-based projects.

Martijn has indeed listed and identified 26 interaction design Patterns that he has grouped under four different categories:
a) Navigation
b) Page Elements
c) Searching
d) Ecommerce

Interaction patterns, if you are not familiar with them include typical interface design items like:

a) Breadcrumb navigation trails
b) Meta Navigation
c) Outgoing Links
d) Split Navigation
e) Repeated Menus

or typical Page and Search elements like:

a) News box
b) List builder
c) Tabbing
d) Simple Search
e) Advanced Search
f) Sitemap

For each one interaction pattern listed a nice and easy to read page provides specific information on the following topics:
a) Problem
b) Use when
c) Solution
d) Why
e) More Examples
f) Known Uses
g) Related Patterns

I find it extremely useful and needed.
Hats to Martijn for an excellent beginning.