Just walking into the office, or taking a break from a frustrating problem and seeing these 30second (or however long) stills has done infinitely more than any motivational poster could or would ever do for me.
Try giving your developers responsibility, autonomy, trust, and respect. You'd be amazed how far a little self-determination and native pride in ones work can go.
And if your developers are incapable of handling autonomy or have no particular desire to take pride in their work, your problems run way deeper than motivation.
And very few interruptions.
Makes me look at big picture and think of possibilities
Here are some things that you can try that will actually have a positive effect:
-Better pay
-Better hours
-The ability to work remotely
-More vacation and sick time, with the encouragement to actually use it
-More autonomy in the jobs that they're doing
Only thing I've ever seen work to raise productivity and motivate the workers is a sincere and firm handed bit of support from the higher ups. Leads, managers, and the rest that would act like regular people, make sure you had what you needed and could feel free to complain. Also higher ups that protected all the workers in the trenches from Client crazyness and subsequent fallout emotions.
The only kind of wall coverings I've seen that made a difference to the people working there was art from people working there, prints, paintings, photographs. Many people have side projects and they'd love to get some viewers.
Apprently it's quite popular amongst industrial designers but I think the advice is relevant enough to most industries.
http://goodfuckingdesignadvice.com/collections/prints/produc...
On a small team, most of our productivity comes in the morning after we've said hello and settled in. Gets real quiet and we all just get in the zone. As the day winds down we loosen up. It's a very pleasurable way of working, for us at least.
I don't think I've ever heard someone say "Wow I really like the motivational posters" but I have seen some that went pretty wrong (and as a result were ineffective).
So my guess is the have high downside and little upside.
That said, nice artwork (no pithy saying), seems to always make the space feel more inviting and comfortable.
What works in our office, obviously this is personal, but we use an open office space so the fact that others are here and working motivates me.