I am on a month to month rental agreement. I gave notice to quit on 9/19/09. I reported the move out date will be on 10/22/09. Can I prorate my rent or must I pay the entire month?

CA is always a but funkier than other states but in most your must give at least a 30 day notice prior to the date your month to month reactivates. Short answer, no. If your situation restarts on the first on the month you are obligated for the entire month. California Tenant Law - Free legal advice for California renters' rights

On a month to month tenancy in CA, you can give notice at any time... so yes, you only need to pay the prorated amount for October.

California Tenants - California Department of Consumer Affairs

See, just like I said always a bit funky compared to there states. Good find Lill