There are a variety of stores that sell these online, but going through all of them can be very time consuming, so I have selected a few very good models below to help save you some time.
Click here to get your Honeywell 50250n Air Purifier from Amazon.comHoneywell offers a few different varities depending on what your needs are.
The Honeywell 18155 usues a permanent HEPA filter which never needs to be replaced, and it is also one of the quietest on the market. This model also works great sitting on a table or sitting on the floor.
The Honeywell HFD-120-Q tower, with oscillating feature. This air purifier has washable air filters so they never need to be replaced. It also does not emmit any ozone so it is good for you and the environment.