So I have never used a decent air filter, but I have done hours of research and this is as good as it gets for < $300.
I picked up one of these and it's in the shipping stage now.
As far as I can tell this is the old 5300 version which is preferred because it comes with a remote that the new 5300 does not come with. This allows for the turning on and off of the PlasmaWave technology (unlike the new 5300 model).
350 sqft Coverage.
CADR (Dust/Smoke/Pollen): 248/236/252
Dust CADR/Watt: 4.1 (>= 2.0 to qualify for EneryStar, so double EneryStar x 2)
Filters are $$ to replace, but they always are for HEPA filters. This model also can fit the long life filter(cleanable from the 5500 model) from the same company.
The following are for the new version, but you can't find the old one anyway.
Review ($199) : http://www.airpurifiersource.com/reviews/winix-5300/
Amazon link ($159) : http://www.amazon.com/Winix-PlasmaWave-5300-Cleaner-Model/dp/B001RUS05E/ref=sr_1_1