MIL gave us a salt rock lamp. It supposedly creates negative ions, which are known to clean and refresh the air in your room. I put it on the bedside table, and turn it on only at night... I use it as a nightlight, due to its warmth orange color tone.
Update on 14 Feb. 2010: I moved the salt rock lamp out the bedroom, just to be safe... supposedly, it can be harmful for people with hypertension (high blood pressure)... hmmm..., from what I heard and read.
Try to avoid the salt rock lamp from direct sunlight because the salt can melt and create a white grainy residue on the table.