Well,you have dozens of options,especially in the zone you live in.
Always flood your sunny spots with Zinnias-they are amongst the most colorful Annuals that enjoy the high heat of summer.
Make certain you wait until the last frost date in your area.
Also make certain that you do not mix your Zinnias too often-They have very bright colors that can make an area too 'busy'.
Marigolds provide awesome color during warmer months.
There's been a lot of excellent recent introductions for spectacular foliage plants such as Hibiscus acetosella 'Red Shield',Perillas,Coleus,and this fun annual vegetable plant Atriplex hortensis'Red'.Spot these all around for filler plants.
Try playing with festive perennial foliage plants
such as Angelica,Persicarias,Fancy leaved Pelargoniums,Artemesias,
and Hostas.
Never overlook natural elements like Ornamental grasses and
Boulders.
But most of all take your time with it,you'll find the experience rewarding.

I love the profusion zinnia, great plants. I did a bed of impatiens at one point and they looked spectacular all summer and they had morning sun. The impatiens are great too because there is no deadheading. I did them in drifts of color.

Diamond frost euphorbia is perhaps the best addition I have seen in the last 2 years. The dainty white flowers are stunning and go well with just about everything. My thrive in full sun or partial shade.