I usually use plastic, microwave safe cookware in the microwave. In addition to being labeled as microwave safe, I also make sure that the cookware is made with safe plastic. The ones that have a triangle with the number five inside on the bottom are made from safe plastic. Other types of plastic are dangerous for health.
I should warn those who use plastic cookware in the microwave however, that the lids of some are actually not microwavable. So it's not enough to check the cookware, the lids need to be checked too.
I recently bought a plastic cookware set and saw that the lids had the non-microwavable sign on it. I was shocked at first, but realized that it's just the lids. The actually cookware is microwavable. It's good to know.