In my mind, there is an undeniable relationship between UI design and graphic design.  They share a similar communication goal and are both concerned with things like layout, color, balance and type.  Whenever I mention that, though, Nate is quick to remind me that, while interaction design may be the adoptive step child of graphic design, its flesh and blood is industrial design.  In the spirit of that relationship, Dan Saffer has started cataloguing interaction inspirations from the real world.  Feeling stumped about an interaction in the software you design?  Find some inspiration at No Ideas But In Things.