If you are in the Denver area, you can see Russian Sage blooming all over. It's extremely drought tolerant loves the sun. The sunnier the better.

Purple Leaf Sand Cherry works well too. Smoketree is similar in color. For me the two are quite interchangeable.

Maximilian sunflower, is a perennial but it gets so large I think of it has a shrub.

My weigela do extremely well. I noticed the other day, I may be getting a second bloom this year (spring is when it has major blooming).

Potentilla give summer blooms for a long time. Prune hard every year and they do pretty good.

Junipers work if you want evergreens.

Please be as specific as possible as to the sun exposure, water available. size of plant, and in general what your expectations are.

Rose of sharon is another option. I have two in a West-facing position and they do very well. They do get big though.

You could plant Pawnee Buttes sand cherry, Ralph's Creeper spreading rose or other hardy roses (including the long-blooming Linda Campbell), lavender (yes, it's a perennial, but it acts like a shrub), Cheyenne mockorange, Tiger Eyes sumac, ninebark or serviceberry, among others.