I don't know of any "good" stand alone dust collectors. The only ones I've had first hand experience with is the grizzly units.....
http://www.grizzly.com/products/Heav...-Control/G9956 and I found it very lacking in the amount of air it moved, and the amount of "crud" it removed.
That's the reason I built my own..... I've never found a commercial one that was worth the money it cost.