Recommend me some good subs around $600.

[kexodusc]

Nightflier - I've heard no fewer than a dozen SVS subs - seems SVS has stolen the torch from Velodyne the past few years, pretty much all my non-DIY ing friends own SVS with a few Paradigms and HSU in the mix. I really like the subs (didn't at first), even the cylinders. THey are very cleverly designed, and well tuned. And they sound better for music than many ported subs do - probably a reason for their popularity - but they are just outclassed for music reproduction by a well designed sealed sub IMO. This isn't so much a knock on SVS, as it is on ported subs in general. They have certain limitations With the exception of possibly dual-chamber reflex designs and some transmission lines, but to my knowledge nobody build those at an affordable level.
The flipside is the output, extension and power for the money SVS delivers - hard to beat. Sealed subs are at a disadvantage to SVS and other porteds in that department unless you spend more money or go very large. They tend to work better in smaller rooms. Porteds tend to work better in larger rooms. Just physics.

I agree with drseid ACI and REL offer much better sounding subwoofers, IMO, but they probably aren't the best compromise for people who use their systems for Home Theater 50% of the time. Power, output, and "fun factor" are a subs biggest selling feature, especially in stores, and when $1200 sealed sub won't play as loud or as low as a $600 sub during Jurassic Park, it's hard to sell. Probably why we don't see many in stores.

FWIW, I'm strongly considering replacing my HT sealed sub with a newer ported sub and moving it to my stereo system for some of these reasons. You don't tow trailers with cars, you don't get good gas mileage with trucks. Ported/sealed subs are similar in that regard - certain design traits lend themselves to certain applications a bit better than others.