What you need are guerilla perennials, a term coined by Holly Scoggins, assistant professor of horticulture at Virginia Tech. Here are a few that will give quick results without much help from you:
Yarrow, 'Powis Castle' artemisia, plumbago, heliopsis, rose mallow (Hibiscus moscheutos), catnip, moss phlox, and coneflower.
Luke Miller, editor
Garden Ideas & Outdoor Living magazine