I've been on a clean air kick for a while. While investing in a HEPA filter is probably a good idea for urban dwellers, I've been working on filling my home with plants from the book How to Grow Fresh Air [1], a book based on some research NASA did on the air purifying abilities of various indoor plants. The book rates each plant by degree of purification, ease of cultivation, and resistance to pests. Add that to some fountains for negative ions, and you have a fresh and stimulating (rather than repressing) home environment.

[1]http://www.amazon.com/How-Grow-Fresh-Air-Plants/dp/014026243...