Try to avoid plants that are not in good condition, as it is a waste of energy to dig a hole for a plant that will not make it. But now can be a good time to get specific items you need if stores are reducing their inventory before winter.
You may, for example, pick up a pricey Japanese maple for a fraction of what it would have cost in the spring. Read each tag carefully, however, to ensure that each plant's zone hardiness, as well as height and width at maturity, suits the intended location.
The size at maturity is key, as it may look perfect now, but in a few years the plant may have grown to a size that your garden cannot accommodate. Plants, unlike furniture, do not remain at the size they are when they are purchased. So unlike interior decorators, gardeners must imagine how much a plant will grow. Some change so dramatically over time that they engulf all of their neighbors. This advice sounds self evident, but all gardeners have to be careful, as we all make this mistake more than we like to admit.
(P.S. I just purchased a plant from a catalog, and when I unwrapped it realized I had been so swept away by the photo of the item that I had forgotten to check if it would grow in my zone. It is hardy only to zone 7, and I live in zone 5.)