While most of us aren't important/good looking enough for anyone to spy on, the Laser Surveillance Defeater allows us to at least pretend for a moment or two. While much of audio surveillance functions by picking up voices through windows, the $70 Surveillance Defeater can jam these signals. Sticking to your window of choice via suction cup, it sends out a cacophony of human frequencies to confound long-distance microphones. Pick yours up today and no one will ever discover that...well...you really don't do anything exciting behind closed doors. [Shomer-tec via inventorspot]
I carry around 2 Soungbugs [gizmodo.com] when I travel. One could use them to do the same thing with an iPod for a fraction of the cost. They don't sound great, but boy is it funny to pipe music through to people having coffee, or making a conference call in a glass room, or to stick on a friends helmet- until they take off riding.
Professional isolation rooms, if they must have windows, use double or triple pained windows and use a pizzo electric tape to do the same effect. One could also use a speaker.
One could also use the cone of silence.