The problem that you will be having is that it is against building code to use single pane windows now. By code, all windows have to be thermal and double paned with low-E glass.
Alas, the single pane is a thing of the past.
But on the bright side you are getting a better window.
Double pane windows provide by far a greater amount of insulation from the outside. Because they contain two panes of glass with a sealed barrier of air between them, they keep cold air out and warm air in. Thus, they are much more efficient in terms of energy saving.
Now is the time of year when you can really see how much energy you can save with replacement windows (Department of Energy estimates put the number around 40%). If you are spending all that money on running your furnace (or air conditioner in the summer) it only makes sense that you should try to keep as much of that conditioned air inside your house.
That all being said, the best glass in the world won’t overcome a sloppy installation job. The window must have the appropriate amounts of weather stripping and the hardware that accompanies the window needs to fit correctly to promote a tight seal.
There are several quality replacement window companies in the metro area. The best way to shop is to go to a show room and find all the qualities you desire, considering looks, ease of maintenance, and type of glass then get three quotes and go from there.
Good luck – although you didn't intend to, you are on the path towards an energy efficient home!