A neighbor actually made those Martha/Country Living-y pumpkin planters, and they look good. It's simple as hollowing them jack o'lantern style then planting grocery store blossoms. The fleamarket table mid-lawn and interplay of planting-and-building color made a frosty morning walk far warmer.
Categories: DIY, Tips & Techniques
Before & After: Emily Henderson Transforms a Senior's Studio Space
Danielle's Charming, Classic Walk-Up
Good Food to Share 
The Big Book of Small, Cool Spaces 
Apartment Therapy Presents 
The Eight-Step Home Cure 
White Enamel Four-P...
On Saying No to Paleo: Why Eating Isn't One Size Fits All
Perfect Summer Cocktail Recipe: Honey Bourbon Lemonade
I do this from time to time. The trick is to spray the inside of the pumpkin with Lysol so it doesn't rot immediately. (Of course, you could probably wipe it with bleach or peroxide too.)
or, you could make them really wonderful by hot gluing dries on top, like this florist in Dallas, famous for it's seasonal pumkins:
www.drdelphinium.com
We just did this for centerpieces for my brother's wedding, using ghost pumpkins, mums, grasses and reeds, and what was left of flowers in my mom's garden. She filled them with dirt but then put a small ball jar in the middle of them with water to hold the fresh cut flowers. The finishing touch was a vine that was flowing out of it that wrapped loosely around the base when it was on the table. Beautiful!