Thanks for writing. One plant that immediately comes to mind is double impatiens. As easy-to-grow as regular impatiens, it offers double flowers in a wide range of colors.
If you have acidic soil, you may also have good luck with camellias; evergreen shrubs with double rose-like flowers in shades of red, pink, and white.
Look for these and other great plants at your local garden center!
---Justin, Senior Garden Editor, BHG.com