Other PG options -- JJ Barea ... Ronnie Price, Anthony Carter, Earl Watson, Carlos Arroyo, Marcus Banks, Earl Boykins and maybe Acie Law depending on whether his Euro contract has an out clause.
I think Nate Robinson is more talented than every player listed after JJ Barea. Nate didn't give a good account of himself last time around in Boston but I think Doc can get a little more out of him in the future.
If Nate was a non-starter as a backup PG and we lost Delonte West, I'd look to Ronnie Price. He'd be my next choice. I have always loved Ronnie's infectious energy, quality defense/rebounding and explosive athleticism.