Do you have speakers already installed into your car or are you trying to do everything from scratch, because if you are trying to better the ones you have first you must view them, and decide how much you want to move up, also you are not going to find the best best speakers without breaking the bank, but you could look for higher wattages.
Because I just installed some speakers in my trunk resently as well, so. I got some for the trunk at walmart some panasonic ones. They are good and i resently ordered some speakers for the front as well. If you are looking for your car to really bump and be real real loud you gonna have to look into get a boxed sub speaker, an amp, and new speakers.