Memphis subs are quite good..
The Studio line sounds awesome..but aren't the best at handling big power..the HP's can handle more than their rated for..sound quite good..and thump..but are $550 for a single 12".. a little pricey to say the least... Eclipse 8700 series subs are without a doubt on par with Memhpis HP's have a 3 year warranty..and cost only $329 each.. also will play a fair bit lower.. these subs in 1.2 cu.ft ported..tuned to 28hz..will deliver awesome sound quality..insanely low bass..and some pretty serious SPL... the new JL 12W3v.2's will as well but won't have the same low end extension....
it's a matter of what you like and how much you wanna spend really..