In the 10" range, I can think of 4 recommendations; 3 I have heard personally and although I haven't heard the 4th, I do own it's bigger brother.
1. You are already familiar with SVS, so you may consider the PB10-ISD (I own the PB12).
2. Wharfedale SW250. I really like this sub. Tight bass, nice looks (not your standard square box...it is teardrop shaped), and comes with a remote that allows you to switch between custom presets. I don't know about most people, but I wish my SVS had this feature. When I switch from DVD to music (or the other way around); I always have to get up and manually change the settings on the back (usually just the gain).
3. Paradigm PW2100. I find this sub marginally better than the SW250 in the HT department but it isn't as musical as the SW250. Both are very close, IMO. Paradigm also has the Seismic 10; which I haven't heard. It has much more power than the PW2100 and goes a little lower. If I am not mistaken, it is also significanlty more expensive than the PW2100.
4. Martin Logan Descent. I don't recall if you listed a budget; this sub is pricey. The box is very compact (22x20x18)yet contains 3 10" drivers in a pyramid configuration. This is probably the best 10" sub I have heard to date.
Granted, I have not heard them all; but out of the countless subs I have heard, these are my personal suggestions.
Good luck!
