Enercon
Edited to say I'll get back after I get some more info.
Second edit: Dana has left Enercon and started his own company, GENREV in Hearne. His yahoo email address is dcaskips (semi spamproofed here). I don't want to post his cell number but if you would like to contact him for an estimate, please either PM me, mail me at the address in my profile, or post an email address and I'll send it to you.
When he was at Enercon, he came out and measured all my windows and supervised the replacement installation, including some custom shaped ones. I will be using him again for more windows.
For those who haven't used Enercon (now a different business but I'm sure this still applies to both Enercon and GENREV), you can replace one window at a time, or a houseful.
I haven't used Enercon since my initial windows replacement binge, so I have nothing negative to say about them.