Never mind the plug-ins;buy some plants

"It is suggested that one [large] houseplant should be allowed for approximately 10 square yards of floor space, assuming average ceiling heights of 8 to 9 feet. This means that you need two or three plants to contribute to good air quality in the average domestic living room of about 20 to 25 square yards.

"Research has shown that these 10 plants are the most effective all-around in counteracting off-gassed chemicals and contributing to balanced internal humidity:

Areca palm
Reed palm
Dwarf date palm
Boston fern
Janet Craig dracaena
English ivy
Australian sword fern
Peace Lily
Rubber plant
Weeping fig"