Don’t forget the shoe-trees!
My perfect nature? Puppies and 19 year-old raver-girls in A&F shirts would never age.
Mosquito bites would feel gooood!
The “rules” of organic chemistry would change in accordance with the answers I provide on tests (I still believe that that diester compound formed via “smoke and mirrors” and not a dieckman condensation).
Drinking beer would make you lean and muscular.
So would drinking Coke and eating chocolate.
Sheri
More colors, much longer nights, and an end to all things that can cause me to itch.
Umm, my underwear?
There would be no such thing as STD’s.
And women would be willing to give it up as easily as men do.
Longer days. 24 hours is way too short.
Alternatively multiple intelligent species. That’d be fun. 
Food never spoiled.
Gotta second that repealing the speed of light limitation suggestion.
As for myself, I’d change the unfortunate fact that “Might makes Right” works so much of the time. 
Or perhaps, alter the rules of human sociology so that in nay culture, people showing definate “Nerdy” or “Geeky” traits, are raised to positions of leadership and power, and revered as living gods. 
Failing that, I’d just make MYSELF a God, so I could change things I disliked at will. (Or does that fall under the “No wishing for more wishes” clause?)
Ranchoth
I would have lazy Verizon, rip out the fiber in my building and put in copper, so I could GET SOME FREAKIN DSL ALREADY!
Also 56k connection gives you a 2 ping.
Thats all
Bodies would get stronger and healthier as you get older and wiser and can think of better things to do with them.