Comment Green Glue (Score 1) 474
Someone else already mentioned Sound Proof Windows, but in my house 90% of the noise comes through the walls, rather than the windows. I discovered this after upgrading my windows, of course.
If I were building from scratch using stick construction, I'd consider using staggered studs.
If I were really motivated, but not building new, I'd use Green Glue and just add that between the existing wall and an additional layer of new drywall.
There's plenty you can do on existing construction, but most of it is expensive, and a pain in the butt. The insulation and caulking you've added probably won't help much, since the exterior is attached directly to studs, to which the interior is also directly attached. It transmits vibrations easily, without regard for your insulation. The staggered studs and the green glue are the best ways I know of for dampening residential noise.