This window box has some really great features.
The Lechuza Balconera Cottage Self Watering Window Box is rustproof, weatherproof, hangs from walls or rails + can be floor planter, has pull-out liner making switching plantings easy, and a water reservoir to extend time between feedings. Window boxes dry out QUICKLY, so this is nice because you can monitor the reservoir levels as well on its indicator. The list of pros go on for this planter.
this is made of lightweight fiberglass.
I really like the look of this box/planter meant to look like stone, yet made of lightweight plastic.
Since boxes dry quickly, watering is a constant task unless you buy the self watering box I included at the beginning of this post. This hose has been a great purchase. Space saver and easily expands to a long length.
A few others for inspiration: