i have Coustic 4x6's in the front and they sound really decent, but if i had to do it all over again i'd get some sony xplod's. they sound good and they aren't all that expensive. i think wal-mart sells them (xplod's) for around $70. i got some pioneer 6.5's in the back that i got for $20 (on sale, usually $30) and they sound really clear. but i'm seriously thinkin about some xplods for $70 in the back.
speaker choices are more of a sound (and wallet) preference. the more u got, the more u spend. anyhow, good luck w/ whatever u choose.