u are gonna have to search for many past posts in this area, but to give u a cliff notes version from my memory, basically:
eibach springs - like 1.6 inches, cheap only liike $300 or so...definitly will effect ride quality away from your stated ride quality goal.
goldline springs - similar to eiback, less agressive lower...only like an inch.
hotchkis spriongs and swaybar setup - from the reviews on this board these will give you a tad more then an "srt8" stance...i think like an inch, u will have to research, but the verdict was that the ride quality was excellent with these...lowering for better handling, but still retiaing the luxury rig mojo. the set is like $600 or so, and install somehwre in the 700-1000 area.
KW coil overs - these are reported as having amazing ride quality, and the added ability to have the stance adjusted to your desires. so you can have them setup with the exact drop you want. this is about a $1200-1400 upgrade from what i remember.
air ride - i dont know much about the airbag thing, but i think its huge cabbage/duckets..