luvtheemcee recommend exactly what I was going to.
The lady who runs Hollywood Poster Frames is Sue Heim and I've had all of my window cards and movie posters framed by her.
She is only opening to the public here in Los Angeles Thurs, Fri and Saturday. The rest of the time she is doing the framing for several studios.
If you buy them in bulk, you get a discount from here. My last order I got about 12 at once.
The really nice thing about her stuff is that you can get UV Non-Glare Plexi Glass and Acid free backing for a fraction of what you'd pay for that at an Aaron Brothers.
She also will do custom size frames at a very affordable rate.
Here is the link to her direct website:
http://www.hollywoodposterframes.com/ I also recommend checking out her eBay auctions as emcee suggested.