This is my personal ugrade and future upgrade list. My goal is to increase power and mpg.
I would go with some 235/65/16 GY Triple Treds .4 inches shorter than stock and a little wider. Nice looking tire as well as areodynamic. Can handle sand, snow, mud. Tirerack has an $80 rebate right now.. $520
An intake gave me 1 mpg increase on the freeway and a decent power increase. $80-$300 on ebay. I found a K&N used for 80.
NGK 7252 plugs gave me another .5 mpg freeway over the Champion coppers I had. $30
The 703 injector upgrade will get you running better as well. I havent done this yet but I will soon. Ive heard this can increase mpg by 1-3 and slightly increase power with better delivery the 4 hole injector has. $200 or less for brand new ones.
SCT tuners and Superchips tuners offers power and economy settings. $300
Full 3'' exhaust with headers will improve everything so Ive heard $1000+
An efan should reduce drag on the engine.