w/out downloading stuff
the add stars cheat. add as many as you can.. and the car cheat of your choice. some heavy metal driving music. and your good to go
p.s dont forget about your fav gun set too. 
you can find the cheats here http://www.cheatcc.com/XBOX360/grandtheftauto4cheatscodes.html
I kill people.
With guns.
References :
When ever i am bored i do this.
Start at the air port and have a massive shoot out untill your stars have really risen, Then make the great get away to the choppers on the middle island once there steal one.
fly it to where road blocks are and get it low enough and blade everyone up.
seems basic but infact a lot of fun.
References :
the add stars cheat. add as many as you can.. and the car cheat of your choice. some heavy metal driving music. and your good to go
p.s dont forget about your fav gun set too.
you can find the cheats here http://www.cheatcc.com/xbox360/grandtheftauto4cheatscodes.html
References :
a pro weekend killer