Coreopsis. One of the easiest-care perennials. Long bloomer, starting up in summer and continuing through autumn. Daisylike flowers bloom in bright yellow, but there are also varieties with golden yellow, pale yellow, pink, or bicolor blooms. Deadhead flowers to encourage additional bloom. Zones: 3-9.
Shooting Star - Shooting star bears delicate, intricate flowers in spring. Unfortunately, this ephemeral goes dormant for the summer after blooming -- so site it with a companion so you don't have a bare spot of soil.