Subwoofer for Magnepan 1.6's

I use a REL Strata III with my Innersound ISIS and am very happy with it. The adjustable crossover is what sold me on it, as well as it's musicallity without being boomy

If you are looking for a great sounding affordable sub without breaking the bank, try the Onix Rocket by Av123.com
/Perpetual Technologies. It comes complete with the room calibration and mic. set-up in a well made, compact, and attractive enclosure. They offer a 30 day free home trial as well. It sells for under $500 and comes in a number of different finishes. It blends very well with faster speakers like the Maggies. I have been very happy with it in my small system, paired with my 3A MM DeCappo i's. It gets down quite deep to 24hz, but does not overwhelm the room with too much boomy, uncontrolled bass like many of the more powerful home theater subs. The automatic room calibration is quite effective at removing the resonant bass peak in my room.

Martin Logans also mate well with planars. Their subwoofers are also compact in size and can produce tight bass.

Thanks for all the good suggestions, should make looking for a sub a fun process...

i ended up going with the rel brittania 3 -- it sounds sweet with my setup...