At a quilt show here in the UK recently, I discovered Wonderfil threads, a Canadian company, that has just started to distribute here. I bought a sample pack to try and am very impressed. They do Invisifil which is a gassed poly 100 wt - I've tried it as bobbin fill and for machine applique and it's great. Up until now I've been a Superior Threads girl but I may just change allegiance... they have all kinds of wonderful decorative threads too, in mouth watering colours - check them out, I'm sure they're available in the US...
http://www.wonderfilonline.com/