Create an engaging and interactive view into Portland's datasets by displaying it on top of the video you see through the camera of your phone. This technique is called Augmented Reality. This would allow you to visually locate nearby services such as bicycle parking, TriMet stops, parks, etc and currently is supported on the iPhone and Google Android platforms.
I am a local iPhone developer and would be very interested to work on this with other mobile developers.
Here is an example application that locates the nearest train station: http://www.gizmodo.com.au/tags/nearest-tube/
You can read more about this technology at: http://en.wikipedia.org/wiki/Augmented_reality