Macro of several glasses of colored water (but that was obvious, wasn't it?). Put the glasses close together and the mutual reflections and refractions make interesting colors & patterns. Adding a circular polarizer to the mix makes it interesting as the different colors - as they reflect from one glass onto another - are affected differently by the CP. Add a change in focal distance and the whole ballgame changes again. Move any glass even a millimeter - and another change. You could make a long term project out of playing with this.
See here for what the setup looks like - http://www.pbase.com/ed_k/image/74587933
PS - the glassware should have some texture or patterns; not just a smooth surface.