I frequent cleanmpg a lot and found this site while looking for aero mods for my 2006 civic LX. Unfortunately it is an auto (my accident at the time prevented me from using manual), but I know I can make some significant gains.
So far I've:
-Purchased a ScanGauge
-Modified license plate to partially block lower grill
-Tires at 44psi (max sidewall)
-Practiced many hypermiling tactics (driving without brakes, pulse and glide, etc.)
Mods I'm working on (mostly aesthetic, but functional):
-Lighter rims (current OEM steel wheels weigh 18lbs and will be going to 14-15lbs each wheel).
-Lowering springs (about 1")
-Tires at 50psi
Future mods:
-Full upper grill block and maybe lower with close supervision to heat build up(extremely dry heat in my city)
-Warm air or Cold air intake (still on the fence about which will be more beneficial).
-Wheel well covers for rear and eventually front when I can find something aesthetically appealing.
-Custom make my own aerodynamic kit from foam or other heat resistant material.
I'll post pics as I progress, but if you have any suggestions please let me know. I'm looking to have fun with this.