[lubujackson]

Interesting that so many of these "unique" sites are ones that are more about the unique person behind them or a vision of an older internet. One that I think is unique on it's own merits:

http://nuggety.com/

A little confusing, but it allows advanced searching across multiple image search sites - set your filters then it shows you all the sites you can search with those settings and deep links to the search results for each one.