I've also heard great things about ACI subs. I wonder if their drivers are made in the USA.
By the way, Hsu subs are designed and built in the USA, too. Oops, just looked at their site and see that thay claim only to be designed and engineered in the USA, so I guess they're manufactured in SE Asia. When I bought mine in 1994 (the models made out of Sonotubes - cardboard cement column forms - they were built in the USA.