I think what is recommended is a component set, if you are planning on keeping the stock amp. Lots of stuff on ebay and kijiji.
There is a company that specializes in building a kickass upgrade using upgrade speakers and keeping the other components stock. Do a seach for Stage 1...
My car stereo sounds like ass, and its all working right
Im putting in all aftermarket stuff for 1/2 the price of a good set of component set of speakers.
Its going to be a lot of work, but all the info is out there if you search.