You can get a lot of inspiration by Google. I put in "narrow hallway" and "narrow hallway decor" and then selected "Images" and got a lot of great ideas. Some of the ones that I particularly like include:
http://blog.purehome.com/2011/hallway-decorating-tips/
Not so keen on the colors (the pink on the floor), but I love the diamond floor pattern and the chair rail.
http://www.desiretoinspire.net/blog/2010/8/6/reader-request-long-narrow-hallway.html
There are quite a lot of good inspirations here. Horizontal stripes will make a space feel wider like the top picture in the right-hand column. The wide ovals also help make the space feel wider in the Eric Roth design (5th row down, right hand column).
http://www.villalagoontile.com/images/installations/VLT-pescado-hall.jpg
As another PP mentioned, flor tiles can be used creatively, such as this one. Not my colors, but with the center solids and the outside a border it does widen the look of the hallway. If you hallway is too narow, make the center one tile wide with the border around the outside and it will still work.
Loads of good ideas out there.