I do all my own framing/matt cutting and have used a mail order company for the last thirty years or so for frames. Way back in the day, they were a small, service oriented business and since the advent of the internet have become one of the best companies I've ever dealt with. You can check out their website..
americanframe.com.
Even when I was a worker bee framing stuff at Michaels Farts and Crap, I use them instead of my employee "discount", which was always more expensive than americanframe. Only drawback to using americanframe is the plexiglass/mat board for one sheets are too large to ship to me here in Germany, luckily I found a local source for the those items. I pretty much use two inch mattes on one sheets but it really depends on how the poster was printed. Over the years I've settled on standard sizes for all my paper with one sheets being 30.5 x 43, half sheets 24 x 30, inserts/triptych 18 x 40, single lobby cards 13 x16. This way if I want to I can easily swap out matted posters and not worry about the frame fitting or not. But there is always stuff that refuse to be fitted into the standard shoe size, so they get the "custom treatment" and a dedicated frame of their own.
