I have bought a number of air purifiers over the years and I have found the ionic pro by sharper image far superior to any others I have ever bought/used. It has no fan so what it may cost you upfront you will recoup in lower electricity bills (and no need to buy filters) ... I bought a cheaper model w/a fan which not only doesnt work as well -- the electricity bill was enormous!
Look for deals for ionic pro -- you dont have to get the latest model. No filters, no fan. I also bought a somewhat cheaper other brand but similar in type to the ionic pro and while it works reasonably well -- it is not as good at ozone output.