AustinAir makes good stuff. I got an IQAir HealthPro Plus for our bedroom and it has worked really well. I breathe a lot better (chronic allergies).
If dust is what you are looking to control, I would recommend getting something that is effective at filtering particles. A strong fan, good construction to minimize air leakage, and HEPA filters for allergens (HEPA-type would be find for just dust) is a good combination. Blue Air, IQAir, Austin Air all do a good job from what I have read.
If you want the lowdown on air purifiers and avoid bogus claims, here are the best resources I have found:
1 - Environmental Protection Agency: Guide to Residential Air Cleaners
2 - Air Purifier Guide: Clean Air Delivery Rate
3 - California EPA: Hazardous Ozone Air Purifiers
4 - Consumer Search: Air Purifier Recommendations
(they just summarize what other people say but they seem to do a good job of it)
Consumer Reports tests some of the models you see in big box retailers but that is only a small number of the available models so I don't think they are all that helpful personally. Plus they don't really tell you their testing methodology. IQAir backs up their claims with laser particle tests which is pretty cool. These instruments are used by Indoor Air Quality professionals to measure the amount of particles in the air down to ridiculously small sizes. IQAir has also won a ton of awards but they are spendy - $700 and up for the model and then around $100/year for filters.
Best thing you can do actually is buy a good HEPA vacuum cleaner. An air purifier will only do so much since dust is heavy and settles onto surfaces.
Hope those resources help.