http://homokaasu.org/rasterbator/
Despite what the name looks like, the site isn’t kinky at all. Basically it will take any image you want, blow it up to any size, and then you can print it out yourself and hang on the wall. Fun for a kids room, or if you print it out on nice enough paper and frame it, could be a sophisticated art piece.
In our old apartment I took one of our wedding photos and printed it on cardstock. I then hung it with blue tack above our fireplace. We received a lot of compliments on the photo.