I love such a hodgepodge of flowers in my garden, it's hard to pick favorites! As others have said, my favorite tends to be whatever is blooming today. :-)
I do especially appreciate tough, drought/heat tolerant plants that don't need much attention once established. And I like a variety of flower forms and foliage. Daisy-shaped Coneflowers, Heliopsis and Black-eyed Susan, and of course Shasta Daisies. Spikes of Salvia, Lavender, and Veronica. Low-growing Thymes and Lamiums, and plants like Rose Campion and Alpine Catchfly that pop bright little blooms above low foliage. Lilies -- daylilies, asiatic lilies, oriental lilies, for a parade of blooms all summer. Blooming shrubs like lilacs and butterfly bush.
Those are just a few favorite summer-bloomers. I love spring-blooming bulbs, especially daffodils, muscari, and species tulips. As they're winding down, the back area of the perennial bed puts on a show with irises and columbines.
Pick 5 favorites? No can do.