It's good to see community-based tagging evolving to include images too. As a photographer, I enjoy browsing gallery sites with a wide variety of images, to get new ideas and explore new perspectives. The sites mentioned in this blog post (WeHeartIt, Fffffound, and Visualize.us) stream pictures that have been tagged by users, so you can explore by serendipity, or drill down by tag.
Tag That Image: Visual Bookmarking Sites Worth Browsing - Bits Blog - NYTimes.com
There are other sites (like ImgFave) mentioned in the comments too, so they're worth reading.