Most of my drive to and from work is on the interstate. My goal is 50 mpg on a usual work week and 40 mpg while hauling kayaks on my roof rack.
Cold air intake since my tach is at over 3000 rpms while on the interstate (+10% mpg as of 04-19-09). Tires at 40 psi (car door says 29/26 psi). Full air dam on upper grill (made of coroplast) and during winter, partial on lower grill (made of styrofoam blocks and duct tape) (+5% mpg as of 02-24-09). Flat stainless steel hubcaps from hubcapmikes (haven't calculated the increase from these yet).
An improved, permanent grill block. 3 peice kamback between roof and trunk that folds up when trunk is opened. Wheel skirts. Steamlined bottom. LED lighting. Light weight kayak trailer. Higher 5th gear (might be able to use 6th gear from Evo transmission). High performance camshaft. Electric A/C compressor. Electric power steering pump. Ultragauge. Not sure when I am going to get to these. Wife has restricted my money spent on this car due to other financial demands.