If anyone is interested - and I'm not necessarily promoting these, but they're what I have. Anyway, I've owned eight subs, and the ones I'm still using are all made by Klipsch. My third sub was a BIC F12 which I had high hopes for, based on the glowing reviews I read online. I struggled with it for four month but never could get it to sound right. Folks here in the BIC thread were no help (long story, ask me if anyone is interested). Then NewEgg had a Klipsch Synergy 12" sub on sale for $260... a bit more than I had paid for the BIC, and so gave it a try... placed it right where I had the F12 and the difference was amazing.
Best thing about the F12 was it was easy to sell. It's very popular among gamers as it really thuds, but if you read up on it you'll find that many owners prefer to turn it off
for music. The Klipsch wasn't what I would call a musical sub, but at least it could play the low notes. Our listening area is rather large... 24x24 with a divider between the LR and dining room, and being box shaped has some issues with standing waves. I liked the Klipsch so much that when Amazon put a similar model on sale I bought a second one and placed it on an adjacent wall and that really evened out the boomy peaks.
The Synergy is still available at http://www.amazon.com/Klipsch-Sub-12...dp/B003VIWK0G/
but be advised that a few ppl have had the amp go out (same thing happened to a few other mfr's... I think ED once had a bad batch, but I'd have to go back and research that to be sure). Anyway I figure I could buy a replacement plate amp if that happens. No biggie. Two years later I still love my twin Sub12's.
So a few months later and NewEgg (again!) has a Klipsch SW350 on sale for $200... http://www.amazon.com/Klipsch-SW-350...dp/B002HWRK9I/
... At the time I was still using an A/R HD510 decorator sub in the family room with some Polk Tsi's for TV and MP3's etc... the A/R was a bit muddy so I sprung for the 350 even though it only has a 8" cone. Wow what a surprise for a small box! Doesn't dive very low but is very musical and is perfect for where we use it. There is also a 10" version available that probably kick's a$$.
Well somewhere along the line I read that Klipsch had been bought by Audiovox (same thing happened to A/R a few years back) and many of their product lines were being discontinued. Again NewEgg offered a batch of Klipsch Reference line speakers on closeout and I picked up a RW-10D 10" sub at $200 for the bedroom, where we have some Polk M40's and 30's. http://www.amazon.com/Klipsch-RW-10D...dp/B000VZ50J0/
Again, they also have a 12" version available. Any of these can probably still be found but the supply has probably dried up and the discounts not as deep as they were a year or two ago. So the reason I'm relaying all this is that any of these subs are currently selling for $350, which if you're about to throw away $200 on a bargain sub, you might end up spending a lot more in the long run when you outgrow it. You may not always get what you pay for but you always pay for what you get.
We don't use the bedroom sub much so I tend to just leave it turned off. One last thing I've learned is that probably the most significant factor in selecting any speaker is room size. Something may sound great in one room but be entirely too weak or overpowering in a different room.
Edit: I guess I should add that Klipsch subs are not known to be particularly good subs, even in the Klipsch threads here on AVS. Personally I don't like much of their product line. But like Polk, Klipsch makes some good speakers, though that doesn't mean that everything they make is going to be good. The best I can say for these subs is that they are the first subs I've owned that did not leave me wanting something better. So as others have said, when you embark on the sub journey, be prepared to go through a few misfires before finding something you like.