http://www.300cforums.com/forums/showthread.php?t=5298
This post helped me out alot. The front dash if you do not want to trim make sure you get the 3.5" size. The front doors are 6x9s, which I have gone with 8" Kicker mids (they sound very good, but need power). The rear deck is also 6x9s but I am sure you could find some 6.5s to fit with a little trimming and a wood spacer.
I went with a 8w7 in the rear deck (sub fires into the cabin), so no rattling. If you are doing 2 Kickers in the trunk, you better get some Dynamat Extreme or something like that for the trunk, rear deck, and sides to stop all the rattles.
I am thinking of trying the JL Audio 3 way set for the front. This will be a 6.5 for the door, 4" in the deck and tweets in the door piller with all the proper crossovers.
There is a small problem if you are using a 4 channel amp for possibly 7 speakers (center, 2 dash, 2 rear deck, 2 doors) without a component set for proper crossover. I know most amps have crossovers, but not all speakers would need the same roll off point. I have started mine, but not done. If you have any questions, please let me know I am not a pro by any means, but I have done the speaker upgrades in this car already.