barrym95838 wrote:
Another would be to steal $0000 -> $007f for I/O, allowing for faster and shorter access. Of course, you're left with only 128 bytes of ZP RAM, but that ought to be enough for anybody!! 
The Rockwell microcontrollers (6501/6541) and WDC's 65C134 map hardware into zero page. It makes the SMB, RMB, BBR and BBS instructions which only support zero page addresses extremely useful for examining and tweaking I/O registers.
Rockwell also relocated the stack to page zero so one continous on chip RAM area serves for stack and user variables. The 65C134 can map its stack to $40-$FF if you clear some control bits.