if you want a nice sub amp go with the jbl, i really like that one for the price. and as for loud subs, i dont know much for spl but my friend has a setup using audiobahn 15s which is painful to the ears. another friend blasts some alpine r type 15s, but i think thats more based on power and setup than the subs specifically. oh, and just so im the first to say anything on this board, check out the lambda.

other recommendations from friends that i cant say i own personally are memphis, and the adire shiva (or its larger brother which i believe is the adire avatar)