[richsherwood]

I would say do something that either a) becomes an integral part of people's day. Something they look forward to seeing every day. Who knows. That could be as simple as inspirational quotes to some gimmick that people will love. Or b) something cryptic. A puzzle like someone else mentioned. One that that's a lot of people involved and creates a lot of buzz. I am not sure what your resources are like but perhaps you could offer a prize at the end. That will have the added benefit of creating some buzz for your company if you so choose to brand yourself with this. Have some fun with this. You could always sell the space but if you're intent on avoiding that then I commend you and wish I was in your position because you could definitely do something awesome with this opportunity.