http://hubblesite.org/
They don't sell the pictures but they allow you to download high resolution photos which you can then head over to your local printing shop to print. Pick up a nice frame of your choosing and Bob's your uncle.
Just go to the
Gallery -->
Picture Album and select what you want from there.
If you select
List Highest Resolution First you'll find all the images with links to downloadable high resolution photo's easier. Select the one you want and you'll see the link
Highest Quality Download Options. There you'll get the highest quality they have available. Ignore the Print-use download options files as they are for home printers.
For example, here is one of the Butterfly Nebula:
http://hubblesite.org/gallery/album/...rn/hires/true/
Get the larger TIFF image (25.40 MB, 3527 x 4110px) as it's uncompressed and would be better for printing.
Any printing shop would be able to print this for you thesedays. Just burn it onto a CD or copy it onto a USB flash drive and take it in. Prices should be reasonable too considering there is more competition with Harvey Norman and other outlets getting in on the action.
That's all there is too it.