Every year I tell myself, "summer is really not that hot in DC." And every year I chastise myself for my short term memory. There's really no other way to dress for both the indoors and outdoors besides layering. A sleeveless top and lightweight pants really do help during my commute (I use commute loosely because mine is about as easy as it gets, except compared to telecommuters). Then after I arrive at work with the AC on full blast, I simply shrug on a cardigan or blazer for the rest of the day.

PS - I'm in love with these navy pants! They're lightweight, wrinkle resistant, with functional pockets, and so comfortable. They are unlined and mine came with a shiny silver button closure (neither of which are deal-breakers). For reference, I'm wearing size 0P. I usually wear regular length in pants, but the petite sizing surprisingly hits me at the perfect spot right above the ankles.