for your zone geraniums or petunias would make a big statement and are very low maintenance. Both are good in full sun or shaded sun. Herbs and veggies are also good in containers. I keep seasonal plants in containers on the porch and rotate them according to the season. I use succulents a lot-kalanchoes, sedums, agaves, echeverias, etc. You could also do something like that-they're very low maintenance.
Grasses also look cool-I have a few containers with different types in them.
Here's a couple of links that will give you some tips:
http://www.gardenguides.com/TipsandTechniques/container.htm
http://www.findarticles.com/p/articles/mi_m1216/is_4_212/ai_115040886
Take a look around the nursery and see what grabs you!
~lee
mother to isabel claire 3.29.00
alena rane 9.19.03