I have an “Inspirations” folder on my computer desktop. It’s full of images that I like, and is organized by month. It worked well for me, but was just a static pile of pictures on my hard drive. Then a friend gave me an invitation to Dropular, which is an exclusive image bookmarking site. I loved it; then it went offline. Then it came back, but remains deep in the throes of development. So I looked elsewhere, and found VisualizeUs. It’s open to anyone, and is a great way to save, find, tag, and sort images you like. It also has a NSFW (Not Safe For Work) filter, which is a feature that remains absent from the current iteration of Dropular. The only sidebar I offer to my hearty recommendation of VisualizeUs is that it can sometimes run on the slow side. But I have a feeling that their infrastructure will see steady improvement as they continue to add new features and receive solid user feedback. Check it out.

There's a whole heap of image aggregator sites such as Dropular around: Ffffound!, VisualizeUs, Yayeveryday, Lookwork etc.. but the greatest so far in my opinion is 'Designspiration' – it is understated and well designed with some subtle features. http://designspiration.net/
Beautiful stuff!!