Uprights is another part I have broken, you get both parts in a set but I have only broken the non-pivoting part (the part that doesnt house the wheel bearings). Some guys have upgraded to Ali but I have only broken a couple and they are cheapish.
I have gone though a couple of HD Dogbones and the drive cups wear away. Dont stock ali rollbars just get people to upgrade to the plastic X bar. Yua may break the odd suspension arm (as Patrick says, its more likely the upper adjustable one). Fuel tanks brake on the odd occaision (a stick went through one of mine and the bolt from the shock on another (turn that sucker around!) or just do the mid tank mod!!)
And yea diff parts!! Stock some shims while your at it although if you dont you may sell more diff gears...
Yup a feww different wheels and tires.
Body shells.
Thats all I can think of right now...

Patrick, I have heard that two ali and one carbon shoe is a good setup, why not try that? Its supposed to cut down on maintenance/prolong life... At least get the vented bell...