How much cash, credit/debit cards for travel to Germany?

I'm visiting Germany for the first time for a week. I'm wondering how much cash I should plan to bring, and whether it's less costly to use a credit card or a debit card for other purchases while I'm there.

when you travel in Europe you don't need a lot of cash. If you have a Visa or Master Card, you easly can take some cash from cash dispensers near the banks. You find almost one on every corner of the street. You don't need dollars, and the value of the dollar against the euro is still decreasing.
Nice holiday