I use Kenwood 3-ways. The sound great over the stock ones, pretty good bass too. Be sure you leave the little foam things in. You wouldn't think so but the help with the bess response immensely.
I now have a seperate amp and sub, but I am still using the Kenwood 6x9s (through a high pass filter so the don't get fed the 20-80hz deep bass) and they still sound great. Only $80 for the pair.