UI Patterns is a great site for inspiration or problem-solving. Perfect for when you need working examples, and also great because it is very web-app focused.
Also helpful: Morville's search patterns. Some are dated now, though.
Last thought on pattern libraries: I read somewhere something that stuck with me. Just because <famous site here> is doing something RIGHT NOW doesn't mean that it is the best way or even the right way. You don't know how it is performing, and you could be modeling your work after someone else's already-failed idea.