Regular car speakers - you can get some name brand ones on ebay new in pair for about $40-$60
Subwoofers/Amp - brands to get if want some bump and place for best prices are ( crutchfield , sonicelectronix , mobilesoundworks.com , and best site where I got my kickers ... hifisoundconnection )...
I have kickers as well and I would have to say go with a Pioneer or Alpine cause they been in the market for the longest and always have the best reviews and outstanding purchase than any other brand