I have wall that I was eventually planning on installing a 3x5 or 4x6 window. I know that the ideal way would be to have two different sheets of glass with a air gap but I'm not sure I have the depth for that.
Anyway to get to the point...i have found a few places (such as where Habitat for Humanity turns in all their left over materials) that sell windows that can be used outdoors. Would this be worth looking into further or should I really be contacting glass cutting places and looking for 1/2" or so?
Thanks

Where are you located? Most of the stuff you would get from Habitat wouldn't be worth your time. I'm a window installer and have quite a few 7/8" insulated.

you know the sound control windows available at Home Depot do a surprisingly good job at isolation. They're more expensive but really do work well. Vinyl clad, two different pane thicknesses.
these:
http://www.milgard.com/products/sound-control-windows/