As for a subwoofer kit, Parts Express has few that are reportedly
very good: part numbers: 300-760 (10" woofer), 300-762 (12" woofer), 300-764 (15" woofer), and they have another 15" kit (300-770), it's not as good as the other three, but it is
cheaper.
PE also has a 'project showcase' that has cabinet specs, component values, and so on, that is, if you wanted to start your woodworking experience by making you speakers.

(it's in the left hand column on the home page, right under "DIY resources")