Here are a couple of websites to take a look at: adire.com and mjacoustics.com. Both have relatively inexpensive subs which have been getting great reviews.
Subwoofer to go with Triangle Celius
I'm searching for a subwoofer to go along with the Triangle Celius. I'm considering going with the Triangle Sub for the match but, searching for other options also. I'll be using the system 60 / 40 for home theater vs. music. I would like to spend about $700 for either a new or used sub. All comments and opinions are greatly appreciated.