Using illustration in web design gives the designer the opportunity to convey there own personal and unique style, and be able to say "this site is mine, and look what I can do". Very few web design styles give an artist this opportunity.
What makes the examples below stand out are not just the beautiful illustrative art work nor the carefully crafted web designs, it is the balance between the two that distinguishes them from the rest. They all manage to be unique in there own right, by highlighting the illustration with carefully positioned content. And when this is a achieved successfully, the effect is amazing and memorable.