;D;D;D
Or install a Chevy Volt motor.
Leaf is Quieter

They had to install noise generators to alert pedestrians that there is a moving car near them. When they were making proposals for the sounds I suggested they use the soundtrack from
http://www.youtube.com/watch?v=_E4erxIeHo8 but they didn't think that was fitting of the car. If you played around with the car you could make it work. There is a speaker and a sound generator, just need a new sound file.
Back to the original question...
Don't forget the bottom of the roof above the headliner
Spray foam does wonders. No joking, it is used on new cars all over the place. They use it sparingly in key locations. But more is generally better. Seal the fenders to the inner fenders/kick panels by the door jams. inside the rear wheel wells (door jam area). The minimal expanding stuff that stays a little soft when cured works best. But careful use or there can be water retention issues.
Air intakes sealed to the hood stop the sound path straight from the engine compartment to the air intake.
Seal all the holes in the floor and firewall, use good grommets.
Closed air cleaner with inlet duct going to the grill
full length exhaust going out the corner behind the rear tire, use heavier gauge tubing in slightly smaller diameter.
Clutched fan works good, electric is even quieter when off but generally noiser when running but a variable fan controller can help a lot. Be sure to get a fan that can actually keep it cool, Spal high performance or factory take off like a Taraus fan.
That is what I can think of right now.