we just had a salesman come to our house trying to sell us a rainbow vaccum, with built in hepa filter. It uses water instead of a bag or canister (we have a central currently but its not too good at cat hair)
It is certaintly powerful and you can turn it on without the vaccum bit where it just acts as an air filiter....but it was almost 3000 dollars..yes three thousand..ummmm I think not.
http://www.rainbowsystem.com/main/
we rented it for a day ( it was in my my hazel helping mommy pics) and...to be honest it did help me sleep better
I let it run in my room for an hour or so before I slept....but still 3,000!!!!!!!