What plants do I use for low maintenance flowerbeds year long?

Perenniels, of course. I did a garden recently, and I alternated tall and short, spring, summer, and fall-blooming, dark and light foliage, and of course I paid attention to color of flowers (not all the pink at one end and yellow at the other end, Haha!!) I used, iris, day lilies, sedum, balloon flowers, shasta daisies, veronica, coreopsis, ajuga, and mums. I live in zone 5, and this was for a western exposure, so hot sun. Yours would depend on the zone and the sun/shade mix, but this system worked really well for me as a method.