PalFee US is a simple to use PayPal calculator for the USA paypal site
When you enter the amount you will be sent via PayPal, you will be shown the fees you will be charge along with the final amount you will get
NEW for V1.1, want to ensure you receive a certain amount after charges? now you can enter the amount you wish to receive you you will be shown what you need to request including the PayPal charges.
PalFee supports all the PayPal rates from 1.9% to 2.9%, simply goto the setting and select the rate you are getting charged
There is a selection for International funds where you will be charged an extra 1% by PayPal.