Look for Vandersteen 2Wq used. Fantastic sub provided your mains go down to 40Hz. I have a pair, purchased used, along with a pair of the M5-HP battery biased crossovers. Deep, clean bass that never gets in the way of higher frequencies, and they disappear into the room. Designed for corner placement, unlike many other subs.
Sub suggestions please
I just got a pair of JBL L100 Classics (I have seen that they are controversial here, but I love the look, and am impressed with the sound...I'm a happy camper). They are connected to the Cambridge CXA61, and I run a Technics SL1600 with a Grado Prestige Green3 cart, and a Cambridge Alva Duo preamp, and Cambridge CD transport (CXC V2). My sub is a Klipsch Reference Series 12", which I like, but it doesn't aesthetically work with the JBLs. I'm considering the REL Classic 98, Sonus Faber Gravis II, or the SVS SB-3000 (I was told I could get it in a walnut veneer, but haven't actually seen that. Walnut is important in this case). Any seconds on one of those options? Any alternates I should consider at $1,500 or less (I am perfectly satisfied with pre-owned)?