Icon resources for designers

I've been using IconMonstr for a few years now and I have to say they consistently create great icons that are clean and readable.  It is great when I'm throwing mocks together, or building my first draft if wireframes.

The UI is searchable and generally you can find something usable after a search or two (it is a German site so they may not have all keywords in there in English),

And the UI is clean and easy to use.