Going to Italy in June and am hearing how some banks charge up to 2% as well as a nominal charge for each ATM transaction.
Does anyone know which banks in CA have best conversion fees?

I cannot specifically answer your question, but in general, it is much better to pay with a credit card than with cash. In general, withdrawing cash from an ATM will be at the current exchange rate plus 4% while credit card transactions are only at 2%.

First, ask YOUR card-issuing bank or the CC folks what it charges in terms of "foreign currency conversion" fees, if anything, so you can make an accurate comparison to some of those "new banks" you've "heard about."

ATM charges for use in other systems vary; mine, for example, incurs a $1.50 charge each time I use it in an "out of system" (i.e., my issuer's) machine.

You will, as Suisse has indicated, get the best rate for purchases if you use a credit card and you'll get the best currency exchange rate if you get cash from an ATM.

Credit Cards--Visa and MasterCard charge a 1% fee. Then the issuing bank of your Visa or MasterCard credit card can charge additional fees if it wants to do so. Some do not charge any additional fee, most charge and additional 2% or 3%.

In my experience, Capital One and MBNA credit cards charge only the 1% VISA and Mastercard fee. I do not understand Suisse's comment about the ATM adding 4% to the exchange rate, however. I have consistently found that ATM transactions (using an ATM card, not a credit card) yield a better rate than credit card transactions.

My bank does not charge a fee for ATM transactions in Italy, and the Italian ATM machines do not add on any fee.

I use my Bank One ATM ($1.25 per transaction) for cash and my USAA Savings Bank V & MC (1% fee and great exchange rates) for food, lodging, gas, etc. My Citi (AA) MC charges 3% and the exchange rate is typically less favorable. I do miss the miles...but.
M