Sue is closing down her online store, but you may still find good deals on Aurifil thread. I prefer the orange spool (50wt 2-ply) for piecing and quilting on my domestic machine (Bernina 1230). Here is a link:
http://www.sewezdesigns.com/Aurifil1.html
This is another online website that has good deals on Aurifil. It usually means buying a pack, though:
http://www.tristan.bc.ca/specials.html
Red Rock has $5 shipping, so sometimes I buy here too:
http://www.redrockthreads.com/aurifil-thread/