With the places I rent from so-called "renter's insurance" is recommended. As far as I understand, the owner of the aircraft generally has hull insurance to cover loss or damage, but there is a tendency in the good ol' USA for the operators to sue you for the liability and loss of revenue which is what the renter's insurance is designed to mostly take of. You've got to love those lawyers!
A good place to start is the AOPA insurance website:
AOPA Aircraft Insurance
Otherwise, google for airplane [sic] renters insurance and go from there. One thing - make sure the coverage is good for non-residents, as most people are willing to take your money and not let you know about these things.
Cheers,
Gareth.