How about a dynamically and randomly generated plot (probably a scatter), generated on pageload and using the Google Charts API.? Something like this logo submission to a previous contest: http://arbitrarian.wordpress.com/2008/02/23/dynamic-logo/
The original idea changed based on the time of day, and the color of one of the lines changed as a function of the time.
This solution obviates the need to decide on a single static logo and color scheme, and a randomly-generated scatter plot seems to be consistent with this site's focus on data.
