Here's some tranny ratio info:
http://ecomodder.com/forum/showthrea...ios-26279.html Basically, the EX sedan and coupe have the worst ratios for mileage, anything would be better. From that link, it looks like the best is found in the HX, CX, and DX/LX hatch.
As far as other mods, I recommend getting an Ultragauge or Scangauge. Then you can see your instant mileage and make sure your grille block isn't making it too hot.