While on the Polaroid theme, here is how I do it.
The frame came from the Dollar store (actually costs me 1.50$... they raised their prices recently... Grrr.).
I use some acid free double sided adhesive squares from Kodak. Since the back of the integral film is essentially plastic, I think acidity isn't really an issue.
I cut a piece of foam core about 1 inch smaller than the print. I just eyeball it making sure it's relatively square.
I tape it to the center of the print. This creates a nice drop shadow under the print. And since it's smaller on all sides, you never get to see it so neatness doesn't count here.
I then tape the foam core to the piece of nice paper using the same tape. This time, I used glossy white laser print paper.
And this is what it looks like...
This time, I put the print on the visual center of the frame (same distance on sides and top). I find it looks better that way.
Custom framing job done on lunch hour just for you guys
[Sorry, image deleted during forum software upgrade. Please re-upload if so inclined.]