A while back, I stumbled across the Yahoo! Design Pattern Library. In the world of usability and interaction, a pattern is defined as:
[An] optimal solution to a common problem within a specific context.
Yahoo! has essentially released internal design patterns, compiled from their own usability testing. The library covers many areas, including interaction, navigation and search. While Yahoo! doesn't represent the epitome of usability, the collection is worth checking out to inform your own design and organizational decisions. Basically, if you get stuck or wonder if there's a standard methodology you're missing, use it as a fallback.
Additionally, Yahoo! released a stencil kit for quickly mocking up interfaces. If you're building services for Yahoo!, it's invaluable. However, most of us aren't. At best, a developer could slap together an interface to better communicate an idea.