Six more? Puerto Rico, DC, British Columbia, Baja California, Cuba, and...?
It's interesting to see all the areas worldwide that have, at one time or another and with varying degrees of seriousness, been proposed as new US states. See:
My guess would be DC, the 4 unincorporated, organized territories ( Guam, Northern Mariana Islands, Puerto Rico, and US Virgin Islands), and American Samoa (the only substantially inhabited unincorporated, unorganized territory).
It's interesting to see all the areas worldwide that have, at one time or another and with varying degrees of seriousness, been proposed as new US states. See:
http://en.wikipedia.org/wiki/51st_state