Kicker, Alpine, Pioneer, Orion, Rockford Fosgate, and a few other brands have great starter subwoofers, but if possible, learn what each brand is good for. Kenwood makes decent starter amplifiers and some headunits, Alpine is known for having quality products all around (headunits, speakers, amplifiers, subwoofers, the works basically), Rockford Fosgate has outstanding amplifiers, and so forth. Some will disagree, but it's all up to you what want, but stay away from Pyle, Boss, and a few others I can't think of off the top of my head.