The first time I made sunglasses, I started with a cylinder, 15 sides, and pulled it into the shape I wanted (I made them sort of semicurcular) and then I copied it, extruded the central face twice (similar to the basic technique of making a cup) and used append polygon to make a hole (This would become the rim of the glasses). Then, I put the model that I had copied from in the middle of the rim, and made them all very skinny (glass sized). I just bent a cube around for the nosepiece, and then I extruded a cube along a curve for the ear-thingies.
Then I mirrored the lens, rim, and the ear-thing across the axis (not combining them) and applied a semi-transparent dark material to the lens (a phong) and a slightly brighter blinn to everything else. I didn't bother to texture anything, but here's a quickie render of a copy I just did for kicks >_>
~I have no idea what I'm doing~