Thanks for writing. You can use just about any shrub that's well suited to the conditions. Some gardeners like varieties such as columnar junipers because they grow tall enough to completely hide the area, but stay narrow (most are less than 5 feet in diameter). Other gardeners prefer taller ornamental grasses. It's really up to you and what plants fit your landscaping style.
Regardless of what you choose, plant them so they're at least 4-5 feet away from your air conditioners so there's plenty of movement and room to work if your units ever need servicing.
---Justin, Senior Garden Editor, BHG.com