This link Architectural Record's Continuing Education Center | Earn AIA Continuing Education Credits Online
has a lot of information about windows and window glass options, including detailed descriptions of all component materials, construction and manufacturing details, with E-rating comparisons and links to various standard-setting and certifying organizations. Be sure to scroll through the multiple pages for all the details.
Here are a couple snippets to answer a few comments/questions I saw asked:
Re: multi panes windows:
"...Argon or krypton (colorless and odorless gases naturally occurring in the atmosphere), is used to fill the airspace between layers of insulating low-E glass... Breather tubes are required on insulating units that will be installed at high altitudes. The breather tubes allow the unit to adjust to changes in pressure. Argon gas is not an option when breather tubes are specified."
Re: framing material
"*Aluminum is light, strong and durable, making it ideal for custom window design. Aluminum frames also require low maintenance. One disadvantage is that they cause conductive heat loss, which affects the U-Factor and decreases energy efficiency. They also allow for condensation buildup..."
"...vinyl offers less structural rigidity or strength by itself and expands and contracts at a rate eight times that of pultruded fiberglass. This leaves vinyl products susceptible to seal failures, stress cracks, fading, chalking and cracking."
"...Pultruded fiberglass frames offer superior energy efficiency because fiberglass incorporates insulating air pockets... The physical properties of pultruded fiberglass do not change through the full temperature cycle up to 350 F. (PVC resins become unstable at 155 F)...However, the rigid make-up of fiberglass may limit design flexibility because curved surfaces are more difficult to produce."
Fwiw, it is dated 2006 and is an advertorial, but I think it is a solid starting point for a good understanding of options. Just keep in mind there is probably newer technology out there too.