My idea is simple, although oddly counter-intuitive in today's grab-and-go culture.  Starbucks should just not offer paper cups, or disposable cups of any kind!  I think a return to the old-fashioned sit-and-drink days is in order.  If Starbucks only sold coffee and tea in ceramic mugs (which they kept and washed and reused) it would cut down on almost all of its waste.  This at first may prove an inconvenience to people on the go, but I think in time it would actually help reverse that effect.  Without so much of a drive-through mentality, people would learn to relax more and allow themselves more time to enjoy Starbucks coffee.  So, this idea has the added bonus of not only helping the environment, but contributing to the well-being of society!

The only hitch would be that Starbucks might have to expand their stores, to accommodate more people dining in.