Close your eyes and take a deep breath...exhale. Now go outside and try it again. It feels a little better, right?! This is because the air is usually much cleaner outside than indoors. Plants are one of the largest contributing factors to clean air! Many plants clean the air by removing harmful toxins.
NASA recently completed a "Clean Air Study" which resulted in a list of plants commonly placed indoors which remove harmful toxins, thus purifying the air. NASA also discovered that the plants helped prevent "sick building syndrome", which is contributed to inadequate ventilation and toxins in the air. Who knew that there was a name for that cramped and stuffy feeling that you have when you are indoors for too long!
The full list of plants and the toxins that they remove can be found on Wikipedia: http://en.wikipedia.org/wiki/List_of_air-filtering_plants
A few of the top performers are: The Boston Fern, Areca Palm, Dracaena, and the English Ivy.
For the full NASA study, please check out http://www.scribd.com/doc/1837156/NASA-Indoor-Plants. Go get a plant :)
Peace and Love,