How much sun does the area have?
Bearded irises are really easy to grow and come back really nicely, growing more blooms every year. They are a bargain, too, as they multiply and need to be divided every few years to keep them healthy. So the divided plants can be moved into other parts of the yard.
Lillies and peonies!
Are you looking to reduce your lawn by carving out a planted area?
You want to plant perennials. They come up every year. You can fill in the bare spots with annuals (those that only bloom/grow once a year)