Epik, Elemental Designs, SVS all have subs under $1000 that are great sounding, even Axiom's lowly EP350 as was mentioned can hold it's own against many of the other subs, pick the one with the price and driver size you want and don't look back. I spent 2 years looking at different subs, it will drive you just as crazy as the decision to buy speakers will.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70