When I think of a wall covered in a large photograph, my mind immediately goes to Scarface...but is that such a bad thing? Yes, it was meant to be over the top and tacky, but it is still freakin' awesome.
There is just something magical about being able to walk over base moldings into a forest, onto a beach, or into a piece of art.
The company Wallpapered let's you select or design your wall art, put in the dimensions of your wall, and receive your art in the mail. Or there is Pixers, which does the same thing. I am sure a google will turn up many more options.
The picture to the left led me to Steve's Wallpaper and Blinds. The site looks budget to the max, so it makes sense they would have some really affordable wall murals for sale. There are a bunch that are less than $100.