Only Necessities Knit Oversized polo tunic can be gotten from a few catalogs sites and are generally speaking inexpensive. I have probably owned at least 15 of these over the last several years.
What I like about them:
They do not wrinkle to badly so you can generally wash and dry them and then just immediately fold them or hang them up.
They come in about 16 colors like navy, pink, black, aqua, red, peach, violet, banana, white, sage, royal blue, royal purple, peach rose etc
They are extremely cool and comfortable in the summer. They are made out of a t shirt like material that is both cotton and knit so they move with you.
They are also 30 inches long.
These can be worn with slacks or jeans.
The only thing I don't like is the darker colors will start to fade after 6 washes or so but then I just wear them around the house to work in when they are too faded and they last quite awhile.
I get these from womanwithin.com