We have a similar cloakroom, with a hidden cistern where you show your waste pipe, although we also have a window behind there too.
We did the front face of the hidden cistern unit with white wood effect kitchen cabinet doors, and used white wood effect laminate worktop for the top. We fitted a row of tile (approx 275mm high) above the worktop, and similarly a single tile above the sink on both walls. The tiles are charcoal black and have a horizontal line of grout every 35mm or so. We did the floor with charcoal tiles, but picked ones which aren't shiny so they don't show any marks or specks of dust etc. We finished with a light blue plain colour for the walls, a ceiling spotlight with two bulbs, and a square mirror on the opposite side from the window, taking up about three quarters of the wall width.
It turned out great, there's nothing we would do differently. I tried to upload a pic but can't figure it out at the mo. If you fancy the idea post back and i'll upload it with the pc.[/img]