Sometimes i get this WOW effect. Last time was for ENSO. Today is for the new imagini service called Christmas Gift Finder which suggests you gift ideas based on a short visual test. The user interface is just stunning (maybe a bit heavy on top right).
I also suggest you take their personality test which is really well done and will draw your visual DNA in a few seconds. You can also compare with millions of other users which is fun.
The user experience registration process and simplicity of the service deserves a full 10/10