DIY stacked wood fireplace facade -- I actually really love this idea even if you don't have a fireplace to begin with. It'd be so simple to zazz-up a brick or stone wall with a faux fireplace to create a gorgeous feature wall.
Plan for repetition. Too many individual plants can be as overwhelming as too many colors. Using the same plant throughout the space creates a sense of rhythm. Chose one to three plants that you can use throughout the flower bed to achieve this effect.