thanks for the input, everyone. i thought about getting the infinity kappas, but questioned whether the accord head unit would be able to safely handle a 2 ohm load.
i did some research and saw that others have had good luck running the boston acoustics s95 speakers, which is slightly less sensitive than the polk audio db690/691. the polk audio ones seems to be a pretty good deal for $90 if it will sound louder with some more low end puch than what the factory rear 6x9's provide.
i think i'll stick with the polk audio one's which are available at circuit city and i can always return them if i do not like the sound quality compared to the factory ones.